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Checking and fixing file systems

Is this the right page?​

  • If you suspect or have been told you may have file system corruption, then you are on the right page! If you were told you have drive errors, you are most likely not in the right place. If the drive appears to be missing, then you are definitely not in the right place! This page is only for file system issues.

  • Your data is stored in files and folders, which are kept in a file system such as XFS, ReiserFS, or BTRFS. File systems are stored on physical and other types of drives. The tools and instructions on this page are ONLY for the maintenance and correction of file system issues, NOT for hardware or other drive issues. If you have any kind of hardware issues or drive errors (read errors, write errors, missing, dropped, or red-balled drive), then this is NOT the right page! You need a syslog for the errors, and SMART reports for the drives.

  • Very important!!! Do NOT run these tools on the parity drive. It does NOT have a file system, and running ANY file system repair tool on your parity drive will likely corrupt it! If you are here because of issues with your Parity drive, PLEASE LEAVE NOW! You are in the wrong place! These tools and instructions are ONLY for data drives formatted with ReiserFS, XFS, or BTRFS.

Drive names and symbols​

  • If you will be using the v6 WebGUI, you don't have to worry about using the right drive symbol, as it will be automatically and correctly selected for you.

  • All others will be working at the command line, and the correct drive symbol is vital! You call your drives by names such as Disk 5, and use it in paths like /mnt/disk5. Linux has other names and symbols internally, for various and important purposes, and your success here will depend on using the right one. When the kernel identifies a drive and sets it up, it may assign SCSI symbols (e.g. sd 2:0:1:0), ATA symbols (e.g. ata7.00), drive device symbols (e.g. sdj, full path /dev/sdj), and Unraid managed drive device symbols (e.g. md5, full path /dev/md5), all of which may refer to the same drive. The SCSI, ATA, and drive device symbols will usually be different from each other, but the disk number, path name, and Unraid managed drive device name will be directly connected. Disk 7 will always be /mnt/disk7 and will always be /dev/md7. However they are not interchangeable, each has to be used in the correct context. Disk 7 is a human-readable label, /mnt/disk7 is a folder, and /dev/md7 is an Unraid managed partition.

  • To get a little more technical, we don't actually store data on drives, we store it in file systems on partitions of those drives. NEVER run a file system repair tool on the drive symbol, always run it on the partition symbol. Which one is the partition symbol? If Disk 3 is a data disk associated with sdj, then the drive symbol is /dev/sdj, and the 2 partition symbols are /dev/sdj1 (add a digit one for the first partition, two for the second, etc) and /dev/md3 (for the Unraid managed drive partition). Both partition symbols refer to exactly the same partition, however I/O access to sdj1 is direct, access to md3 goes through the Unraid parity management.

  • Why is this important for us to understand? Parity protection is preserved when the Unraid managed device symbols are used, NOT when the Linux device symbols are used. If a drive is sdj and has a ReiserFS formatted partition on it at sdj1 and its array name is Disk 5, then there are 2 ways to check/repair its file system.

  • reiserfsck --fix-fixable /dev/sdj1 will fix the file system of the first partition of the drive, but parity won't be updated, parity will become invalid

  • reiserfsck --fix-fixable /dev/md5 will do exactly the same thing as the command above, EXCEPT the parity protection will be maintained, parity will stay valid

  • Note: NEVER run the first command on /dev/sdj, as it will likely corrupt it. ALWAYS run it on the partition, either /dev/sdj1 or /dev/md5.

  • These file system repair tools can be run against any partition with the appropriate file system, not just Unraid data drives. So if the drive you want to check or repair is the Cache drive or any other drive that is not part of the Unraid array, then parity is irrelevant, and you would run the repair tool on the normal partition device symbol, e.g /dev/sdj1. The examples in the sections below however will assume the drive is part of the array and you want to preserve parity protection. Adapt the instructions as needed for non-array drives.

Which section?​

  • Because the instructions are different depending on how your drive is formatted AND which version of Unraid you are running, this page is divided into 5 sections. Please follow only the instructions in the correct section for your drive.

  • If you are running Unraid v6, you can use the WebGUI to check and fix the file system of any data drive. Unless you prefer to work at the command line, go to Checking and fixing drives in the WebGUI.

  • If you are running Unraid v4 or v5 or prefer working at the command line -

Checking and fixing drives in the WebGUI​

The instructions here are designed to check and fix the integrity of the file system of a data drive, while maintaining its parity info.

Preparing to test​

  • The first step is to identify the file system of the drive you wish to test or repair. If you don't know for sure, then go to the Main page of the WebGUI, and click on the name of the drive (Disk 3, Cache, etc). Look for File system type, and you will see the file system format for your drive (should be xfs, reiserfs, or btrfs).
  • If the file system is XFS or ReiserFS (but NOT BTRFS), then you must start the array in Maintenance mode, by clicking the Maintenance mode check box before clicking the Start button. This starts the Unraid driver but does not mount any of the drives.
  • If the file system is BTRFS, then make sure the array is started, and NOT in Maintenance mode.
  • Important note! Drives formatted with XFS or ReiserFS must be checked and repaired in Maintenance mode. Drives formatted with BTRFS cannot be checked or repaired in Maintenance mode! They must be checked and repaired with the array started in the regular mode.
  • From the Main screen of the WebGUI, click the name of the disk that you want to test or repair. For example, if the drive of concern is Disk 5, then click on Disk 5. If it's the Cache drive, then click on Cache.
  • You should see a page of options for that drive, beginning with various partition, file system format, and spin down settings. The section following that is the one you want, titled Check Filesystem Status. There is a box with the 2 words Not available in it. This is the command output box, where the progress and results of the command will be displayed. Below that is the Check button that starts the test or repair, followed by the options box where you can type in options for the test/repair command. The options box may already have default options in it, for a read-only check of the file system. For more help, click the Help button in the upper right.

Running the test​

  • The default for most file system formats (XFS and ReiserFS) is a read-only check of the file system, with no changes made to the drive.
    • If the file system is ReiserFS, then the options box will be blank initially, which implies the --check option. Always begin a ReiserFS drive test session with the --check option!
    • If the file system is XFS, then the options box will contain the -n option (it means check only, no modification yet). We recommend adding the -v option (it means "verbose" for greater message display), so add a v to the -n, making it -nv.
    • If the file system is BTRFS, then you want the scrub command, not the Balance command. The options box should already have the recommended options in it.
  • Once the options are correct, click the Check button to start the operation.
  • The progress and results will be displayed, and you will review them, and decide what action to take next. It is necessary to refresh the screen periodically, using the Refresh button underneath it or your browser's refresh button or keystroke, until the display indicates the test or repair is complete.
  • If the results display a successful test, with no corruptions found, then you are done! Skip down to After the test and repair.

Running the repair​

  • If however issues were found, the display of results will indicate the recommended action to take. Typically, that will involve repeating the command with a specific option, clearly stated, which you will type into the options box (including any hyphens, usually 2 leading hyphens).
  • Then (if not BTRFS) click the Check button again to run the repair.
  • Progress and results will again be displayed, and it's possible that you will have to run it again, with perhaps a different option. If the repairs were successful, it's recommended to run the read-only check one more time, to verify all is well now.

For ReiserFS drives​

  • For more info on the reiserfsck tool and its options, see reiserfsck. There is also more information and some warnings about reiserfsck options in the Running reiserfsck section below.
  • Important! If you are instructed to rerun the repair with the --rebuild-tree option, then PLEASE read the warnings in the Running reiserfsck section below!
  • Important! If you are instructed to rerun the repair with the --rebuild-sb option, then you cannot continue here in the WebGUI! You will have to follow the instructions in the Drives formatted with ReiserFS using Unraid v5 or later section below.

For XFS drives​

For BTRFS drives and pools​

  • Use the scrub command. Use your best judgement, we have little experience yet. Do read the Drives formatted with BTRFS section below.
  • For more info on the scrub command and its options, see btrfs scrub.
  • Unfortunately, the scrub command can detect but not fix errors on single drives. If errors are detected, you will want to go to the Redoing a drive formatted with BTRFS section.
  • If it's a drive pool, the scrub command can fix certain but not all errors. So far there is not a reliable BTRFS tool that can fix ALL possible errors. If the result indicates that there are still uncorrectable errors, then you will have to copy off all data and reformat the drive or pool anew (see Redoing a drive formatted with BTRFS).
  • Unraid is committed to staying up-to-date with BTRFS development, so once better tools are ready, they will be available here too.

Running the repair (continued)​

  • During and at the conclusion of the command, a report will be displayed, in the command output box. If errors are detected, this report may specify additional actions to take. For XFS and BTRFS, we don't yet have much expertise to advise you. Use your best judgement. Most of us will probably do whatever it suggests we do.

  • If your file system has only minor issues, then running the first option suggested should be all that is necessary. If it finds more significant corruption, then it may create a lost+found folder and place in it the files, folders, and parts of files it can recover. It will then be up to you to rename them and restore those files and folders to their correct locations. Many times, it will be possible to identify them by their contents and size.

  • Note: If the repair command performs write operations to repair the file system, parity will be maintained.

After the test and repair​

  • If you are in Maintenance mode, you can resume normal operations by stopping the array, then restarting the array with the Maintenance mode check box unchecked.

Additional comments​

  • These test and repair tools may take a long time on a full file system (several minutes to a half hour, or more).

  • If there was significant corruption, then it is possible that some files were not completely recovered. Check for a lost+found folder on this drive, which may contain fragments of the unrecoverable files. It is up to you to examine these and determine what files they are from, and act accordingly. Hopefully, you have another copy of each file. When you are finished examining them and saving what you can, then delete the fragments and remove the lost+found folder. Dealing with this folder does not have to be done immediately. This is similar to running chkdsk or scandisk within Windows, and finding lost clusters, and dealing with files named File0000.chk or similar. You may find one user's story very helpful, plus his later tale of the problems of sifting through the recovered files.

Drives formatted with XFS​

  • Note: for more info on the xfs_repair tool and its options, see xfs_repair.
  • The xfs_repair instructions here are designed to check and fix the integrity of the XFS file system of a data drive, while maintaining its parity info.

Preparing to run xfs_repair​

  • Start the array in Maintenance mode, by clicking the Maintenance mode check box before clicking the Start button. This starts the Unraid driver but does not mount any of the drives.

Running xfs_repair​

  • Now you are ready to run the XFS file system test. At the console or in a terminal session with SSH or Telnet, type this: (Note: the following example refers to Disk 1, as /dev/md1. You will need to substitute the correct drive for your case. For example, if it is your Disk 5 that you are testing, then substitute md5 for md1.)
xfs_repair -v /dev/md1

  • During and at the conclusion of the xfs_repair command, a report will be output. If errors are detected, this report may specify an additional action to take. We don't yet have much expertise to advise you about this. Use your best judgement. Most of us will probably do whatever it suggests we do.

  • If your file system has only minor issues, then running xfs_repair -v should be all that is necessary. If it finds more significant corruption, then it may create a lost+found folder and place in it the files, folders, and parts of files it can recover. It will then be up to you to rename them and restore those files and folders to their correct locations. Many times, it will be possible to identify them by their contents and size.

  • Note: If xfs_repair performs write operations to repair the file system, parity will be maintained.

After running xfs_repair​

  • If you are in Maintenance mode, you can resume normal operations by stopping the array, then restarting the array with the Maintenance mode check box unchecked.

Additional comments​

  • The xfs_repair tool may take a long time on a full file system (several minutes to a half hour, or more).

  • If the xfs_repair command fails, and we're hearing numerous reports of this(!), then you will have no recourse but to redo the drive. Use the instructions in the Redoing a drive formatted with XFS section below. We're sorry, we hope there will be better XFS repair tools some day!

  • If there was significant corruption, then it is possible that some files were not completely recovered. Check for a lost+found folder on this drive, which may contain fragments of the unrecoverable files. It is up to you to examine these and determine what files they are from, and act accordingly. Hopefully, you have another copy of each file. When you are finished examining them and saving what you can, then delete the fragments and remove the lost+found folder. Dealing with this folder does not have to be done immediately. This is similar to running chkdsk or scandisk within Windows, and finding lost clusters, and dealing with files named File0000.chk or similar. You may find one user's story very helpful, plus his later tale of the problems of sifting through the recovered files.

  • If you get an error indicating something like trouble opening the file system, it may indicate that you attempted to run the file system check on the wrong device name. For almost all repairs, you would use /dev/md1, /dev/md2, /dev/md3, /dev/md4, etc. If operating on the cache drive (which is not protected by parity), you would use /dev/sdX1 (note the trailing "1" indicating the first partition on the cache drive).

  • If you want to test and repair a non-array drive, you would use the drive's partition symbol (e.g. sdc1, sdj1, sdx1, etc), not the array device symbol (e.g. md1, md13, etc). So the device name would be something like /dev/sdj1, /dev/sdx1, etc.

Redoing a drive formatted with XFS​

  • If you are here because the XFS repair tool has failed you(!), then the best we can recommend is to save the data, reformat, and restore the data (NOT a desirable course of action)!
  1. Do your best to copy off everything you can, to a safe place. If something important is absolutely needed and still inaccessible, try File Scavenger or a live CD of TestDisk.
  2. Change the file system format for the drive to ReiserFS (just to reset the formatting, it's temporary and fairly quick)
  3. Start the array and format the drive
  4. Stop the array
  5. Change the file system format for the drive to XFS again
  6. Start the array and format the drive again
  7. Copy back everything you saved
  • It's certainly not a welcome method, but it does produce a fresh and clean XFS format. (The write-up above has not been tested by this author. If corrections are needed, please do them, or PM RobJ with the corrections or suggestions.)

Drives formatted with BTRFS​

  • We're sorry, but we don't have enough experience yet with the scrub command. We recommend reading through this section, then either using the WebGUI to possibly repair a drive formatted with BTRFS, or if you are comfortable at the command line, checking out the scrub command and its options, see btrfs scrub below. But ultimately, if errors are found, you may have to redo the drive.
  • Unfortunately, the scrub command can detect but not fix errors on single drives. It can only fix errors on pooled drives. If this is a single drive and errors are detected, you will want to go to the Redoing a drive formatted with BTRFS section.
  • If it's a drive pool, the scrub command can fix certain but not all errors. So far there is not a reliable BTRFS tool that can fix ALL possible errors. If the result indicates that there are still uncorrectable errors, then you will have to copy off all data and reformat the drive or pool anew (see Redoing a drive formatted with BTRFS).
  • Unraid is committed to staying up-to-date with BTRFS development, so once better tools are ready, they will be available here too.
  • --- work in progress ---

Experimental BTRFS recovery​

  • If you consider yourself an advanced user (or desperate!), here are some advanced tools that *may* help (or may make things worse!)

  • *Important Mounting Note: The repair tools for ReiserFS and XFS require the drives to be unmounted, so to use their repair tools, you start the array in Maintenance mode. The btrfs scrub command requires the drive to be *already* mounted, so you first start the array in regular mode, NOT in Maintenance mode. The other BTRFS tools mentioned here may or may not require the drive to be mounted, so read their instructions carefully. If the tool requires the drive to be unmounted, then start the array in Maintenance mode. If the tool requires the drive to be mounted, then start the array in regular mode.*

  • The first tool you use should be the btrfs scrub command mentioned above, see btrfs scrub below.

  • There is a BTRFS restore tool, that *may* be able to recover more data from your drive. It works in a read-only mode so it is safe to use. Please see the btrfs restore wiki page.

  • The very last resort tool is btrfs check --repair. It's reported to fix some issues some of the time, but with a good chance it will make others worse! You have been warned! Please see the btrfs check --repair wiki page.

  • General recommendation - try btrfs scrub first. If it fails to completely fix everything, then redo the drive using the following procedure, using btrfs restore if needed.

Redoing a drive formatted with BTRFS​

  • Note: the following is for a single drive formatted in BTRFS, not for a drive pool. For a pool, you will have to adapt it, until we add adapted instructions. Sorry!
  • BTRFS repair tools aren't very good yet. If you give up on the scrub command mentioned above, then the best we can recommend is to save the data, reformat, and restore the data (NOT a desirable course of action)!
  • Note: if this is a single drive, we recommend either adding another drive and making it a drive pool, or switching to XFS, becausebtrfs scrubcannot fix single drives.
  1. Do your best to copy off everything you can, to a safe place. If something important is absolutely needed and still inaccessible, try btrfs restore
  2. Change the file system format for the drive to ReiserFS (just to reset the formatting, it's temporary and fairly quick)
  3. Start the array and format the drive
  4. Stop the array
  5. Change the file system format for the drive to BTRFS again (if it's a single drive, consider changing to XFS, we recommend it)
  6. Start the array and format the drive again
  7. Copy back everything you saved
  • It's certainly not a welcome method, but it does produce a fresh and clean format. (The write-up above has not been tested by this author. If corrections are needed, please do them, or PM RobJ with the corrections or suggestions.)

Drives formatted with ReiserFS using Unraid v5 or later​

  • Note: for more info on the reiserfsck tool and its options, see reiserfsck.

  • Note2: Unraid data disks formatted with ReiserFS use ReiserFS version 3.6.

  • This section is only for users who are running Unraid v5.0-beta8d or later. If you are running an earlier version, including all Unraid v4, please go to the next section, Drives formatted with ReiserFS using Unraid v4.

  • The reiserfsck instructions here are designed to check and fix the integrity of the Reiser file system of a data drive, while maintaining its parity info.

  • Note: the following examples refer to Disk 1, as /dev/md1. You will need to substitute the correct drive for each case. For example, if it is your Disk 5 that you are testing, then substitute md5 for md1, in all of the instructions below.

Preparing to run reiserfsck​

  • Start the array in Maintenance mode, by clicking the Maintenance mode check box before clicking the Start button. This starts the Unraid driver but does not mount any of the drives.

Running reiserfsck​

  • Now you are ready to run the Reiser file system test. (Note: --check is the default option, not strictly required, but included here for clarification.) At the console or in a terminal session with SSH or Telnet, type this:

    reiserfsck --check /dev/md1 [answer with the word **Yes**
     when prompted, do not type **yes** or **YES**, but **Yes**
     (capital **Y** and lower case **es**)]*

  • At the conclusion of the reiserfsck --check command, a report will be output. If errors are detected, this report may specify an additional action to take. The most common ones are to re-run reiserfsck specifying the --fix-fixable switch or the --rebuild-tree switch, for example:

    reiserfsck --fix-fixable /dev/md1 [answer with **Yes**
     when prompted. (capital **Y** and lower case **es**)]

  • If your file system has only minor issues, then running reiserfsck --fix-fixable should be all that is necessary.

  • Important Note!!! Do NOT run reiserfsck with the --rebuild-sb or --rebuild-tree options, unless you are instructed to by the output of a previous run of reiserfsck or by an expert user! They are last-resort options, to repair a severely damaged Reiser file system, and recover as much as possible. They rarely repair the system to perfection, and there may be a little data loss. They do a great job, and make the drive usable again, but it's possible files may be lost or damaged, or moved into the lost+found folder. The --rebuild-tree option will almost always create a lost+found folder and place in it the files, folders, and parts of files it can recover. It will then be up to you to rename them and restore those files and folders to their correct locations. Many times, it will be possible to identify them by their contents and size.

  • Important Note #2!!! If the option --rebuild-sb is suggested, then please see the Rebuilding the superblock section below, and follow its instructions VERY CAREFULLY. The --rebuild-sb option requires answers that must be PERFECT! If you are unsure about anything, consider asking for assistance on the Unraid forums.

  • Note: If reiserfsck performs write operations to repair the file system, parity will be maintained.

After running reiserfsck​

  • If you are in Maintenance mode, you can resume normal operations by stopping the array, then restarting the array with the Maintenance mode check box unchecked.

Additional comments​

  • The reiserfsck tool may take a long time on a full file system (several minutes to a half hour, or more). Also re-mounting the disk can take up to 15 seconds or so.

  • If you were instructed to use special parameters such as --fix-fixable and --rebuild-tree, then it is possible that some files were not completely recovered. Check for a lost+found folder on this drive, which may contain fragments of the unrecoverable files. It is unfortunately up to you to examine these and determine what files they are from, and act accordingly. Hopefully, you have another copy of each file. When you are finished examining them and saving what you can, then delete the fragments and remove the lost+found folder. Dealing with this folder does not have to be done immediately. This is similar to running chkdsk or scandisk within Windows, and finding lost clusters, and dealing with files named File0000.chk or similar. You may find one user's story very helpful, plus his later tale of the problems of sifting through the recovered files.

  • If you get an error that says reiserfs_open: the reiserfs superblock cannot be found on /dev/sdX. Failed to open the filesystem. it usually indicates you attempted to run the file system check on the wrong device name. For almost all repairs, you would use /dev/md1, /dev/md2, /dev/md3, /dev/md4, etc. If operating on the cache drive (which is not protected by parity), you would use /dev/sdX1 (note the trailing "1" indicating the first partition on the cache drive).

  • If you want to test and repair a non-array drive, you would use the drive's partition symbol (e.g. sdc1, sdj1, sdx1, etc), not the array device symbol (e.g. md1, md13, etc). So the device name would be something like /dev/sdj1, /dev/sdx1, etc.

Drives formatted with ReiserFS using Unraid v4​

  • Note: for more info on the reiserfsck tool and its options, see reiserfsck.

  • Note2: Unraid data disks formatted with ReiserFS use ReiserFS version 3.6.

  • This section is only for users who are running any version of Unraid prior to v5.0-beta8d, including all Unraid v4 versions. If you are running a later version, please go to the previous section, Drives formatted with ReiserFS using Unraid v5 or later.

  • The reiserfsck instructions here are designed to check and fix the integrity of the Reiser file system of a data drive, while maintaining its parity info.

  • Note: the following examples refer to Disk 1, as /dev/md1. You will need to substitute the correct drive for each case. For example, if it is your Disk 5 that you are testing, then substitute md5 for md1, and disk5 for disk1, in all of the instructions below.

Preparing to run reiserfsck​

    cd [this will make sure you are in the /root directory]
    samba stop [all your shares will disappear from network]
    umount /dev/md1 ['md1' corresponds to disk1, 'md2' to disk2, etc. note: it is 'umount', not 'unmount']
  • *Note: you will not be able to unmount the disk if it is "busy." A disk is busy if any processes are using it, or referencing files/folders on it. If the "umount" command is not successful, you will need to stop any add-on process you might have running that are referencing the disk before you can unmount it. If you have "changed directory" to it, you must log off, or "cd" elsewhere (off the disk) before the "umount" will succeed.*

Running reiserfsck​

  • Now you are ready to run the Reiser file system test. (Note: --check is the default option, not strictly required, but included here for clarification.) At the console or in a terminal session with SSH or Telnet, type this:
    reiserfsck --check /dev/md1
      [answer with the word **Yes** when prompted, do not type **yes** or **YES**,
      but **Yes** (capital **Y** and lower case **es**)]
  • At the conclusion of the reiserfsck --check command, a report will be output. If errors are detected, this report may specify an additional action to take. The most common ones are to re-run reiserfsck specifying the --fix-fixable switch or the --rebuild-tree switch, for example:
   reiserfsck --fix-fixable /dev/md1
     [answer with **Yes** when prompted. (capital **Y** and lower case **es**)]

  • If your file system has only minor issues, then running reiserfsck --fix-fixable should be all that is necessary.

  • Important Note!!! Do NOT run reiserfsck with the --rebuild-sb or --rebuild-tree options, unless you are instructed to by the output of a previous run of reiserfsck or by an expert user! They are last-resort options, to repair a severely damaged Reiser file system, and recover as much as possible. They rarely repair the system to perfection, and there may be a little data loss. They do a great job, and make the drive usable again, but it's possible files may be lost or damaged, or moved into the lost+found folder. The --rebuild-tree option will almost always create a lost+found folder and place in it the files, folders, and parts of files it can recover. It will then be up to you to rename them and restore those files and folders to their correct locations. Many times, it will be possible to identify them by their contents and size.

  • Important Note #2!!! If the option --rebuild-sb is suggested, then please see the Rebuilding the superblock section below, and follow its instructions VERY CAREFULLY. The --rebuild-sb option requires answers that must be PERFECT! If you are unsure about anything, consider asking for assistance on the Unraid forums.

  • Note: If reiserfsck performs write operations to repair the file system, parity will be maintained.

After running reiserfsck​

   mount /dev/md1 /mnt/disk1 [important to match up the 'md1' with 'disk1', 'md2' with 'disk2', etc.]
   samba start [all shares should again be visible]

Additional comments​

  • The reiserfsck tool may take a long time on a full file system (several minutes to a half hour, or more). Also re-mounting the disk can take up to 15 seconds or so.

  • If you were instructed to use special parameters such as --fix-fixable and --rebuild-tree, then it is possible that some files were not completely recovered. Check for a lost+found folder on this drive, which may contain fragments of the unrecoverable files. It is unfortunately up to you to examine these and determine what files they are from, and act accordingly. Hopefully, you have another copy of each file. When you are finished examining them and saving what you can, then delete the fragments and remove the lost+found folder. Dealing with this folder does not have to be done immediately. This is similar to running chkdsk or scandisk within Windows, and finding lost clusters, and dealing with files named File0000.chk or similar. You may find one user's story very helpful, plus his later tale of the problems of sifting through the recovered files.

  • If you get an error that says reiserfs_open: the reiserfs superblock cannot be found on /dev/sdX. Failed to open the filesystem. it usually indicates you attempted to run the file system check on the wrong device name. For almost all repairs, you would use /dev/md1, /dev/md2, /dev/md3, /dev/md4, etc. If operating on the cache drive (which is not protected by parity), you would use /dev/sdX1 (note the trailing "1" indicating the first partition on the cache drive).

  • If you want to test and repair a non-array drive, you would use the drive's partition symbol (e.g. sdc1, sdj1, sdx1, etc), not the array device symbol (e.g. md1, md13, etc). So the device name would be something like /dev/sdj1, /dev/sdx1, etc.

Tools

xfs_repair​

Syntax​
  • The filesystem to be repaired must be unmounted, otherwise, the resulting filesystem may be inconsistent or corrupt. For Unraid, start the array in Maintenance mode.
xfs_repair [ -dnvLP ] device
xfs_repair -V

Source: derived from Linux man page (there are many more options, but probably too dangerous for our use)

Description​
  • xfs_repair repairs corrupt or damaged XFS filesystems (see xfs(5)). The filesystem is specified using the device argument which should be the device name of the disk partition or volume containing the filesystem. If given the name of a block device, xfs_repair will attempt to find the raw device associated with the specified block device and will use the raw device instead.
Options​
  • -n
    • No modify mode. Specifies that xfs_repair should not modify the filesystem but should only scan the filesystem and indicate what repairs would have been made.
  • -v
    • Verbose output.
  • -V
    • Prints out the current version number and exits.
  • -d
    • Repair dangerously. Allow xfs_repair to repair an XFS filesystem mounted read only. This is typically done on a root filesystem from single user mode, immediately followed by a reboot.
  • -L
    • Force Log Zeroing. Forces xfs_repair to zero the log even if it is dirty (contains metadata changes). When using this option the filesystem will likely appear to be corrupt, and can cause the loss of user files and/or data.
  • -P
    • Disable prefetching of inode and directory blocks. Use this option if you find xfs_repair gets stuck and stops proceeding. Interrupting a stuck xfs_repair is safe.
Notes​

  • Disk Errors: xfs_repair aborts on most disk I/O errors. Therefore, if you are trying to repair a filesystem that was damaged due to a disk drive failure, steps should be taken to ensure that all blocks in the filesystem are readable and writeable before attempting to use xfs_repair to repair the filesystem. A possible method is using dd(8) to copy the data onto a good disk.

  • lost+found: The directory lost+found does not have to already exist in the filesystem being repaired. If the directory does not exist, it is automatically created if required. If it already exists, it will be checked for consistency and if valid will be used for additional orphaned files. Invalid lost+found directories are removed and recreated. Existing files in a valid lost+found are not removed or renamed.

  • Corrupted Superblocks: XFS has both primary and secondary superblocks. xfs_repair uses information in the primary superblock to automatically find and validate the primary superblock against the secondary superblocks before proceeding. Should the primary be too corrupted to be useful in locating the secondary superblocks, the program scans the filesystem until it finds and validates some secondary superblocks. At that point, it generates a primary superblock.

Examples​
  • These are just examples, replace drive ID with the correct drive symbol, either an md number (md2, md15, etc) or an sd symbol (sdc1, sdj1, etc).
  • xfs_repair -v /dev/md3 → tests and reports, making changes when necessary
  • xfs_repair -nv /dev/sdc1 → tests and reports without making changes
  • xfs_repair -V → displays version and exits
  • xfs_repair → displays options and exits
  • Note: As far as I can tell, these are the ONLY options we should be using.

btrfs scrub​

For a full description, please see the man page for scrub.

Syntax​
  • The filesystem to be repaired must be mounted first. For Unraid, start the array as normal, NOT in Maintenance mode!
btrfs scrub start [-BdqrR] `<path>`{=html}\|`<device>`{=html}
  • Start a scrub on all devices of the filesystem identified by <path> or on a single <device>.
  • Without options, scrub is started as a background process. Scrubbing involves reading all data from all disks and verifying checksums. Errors are corrected along the way IF POSSIBLE.
  • Unfortunately, the scrub command can detect but not fix errors on single drives. If errors are detected, you will want to go to the Redoing a drive formatted with BTRFS section.
  • If it's a drive pool, the scrub command can fix certain but not all errors. So far there is not a reliable BTRFS tool that can fix ALL possible errors. If the result indicates that there are still uncorrectable errors, then you will have to copy off all data and reformat the drive or pool anew (see Redoing a drive formatted with BTRFS).
Options​
  • -B
    • Do not run in background; print scrub statistics when finished.
  • -d
    • Print separate statistics for each device of the filesystem (-B only).
  • -q
    • Quiet. Omit error messages and statistics.
  • -r
    • Read only mode. Do not attempt to correct anything.
  • -R
    • Raw print mode. Print full data instead of summary.
Examples​

Important Note! These are untested yet!

These are just examples, replace drive ID with the correct drive symbol, either cache or an md number (md2, md15, etc) or an sd symbol (sdc1, sdj1, etc).

  • btrfs scrub start -B /dev/md3 → tests and reports, making changes when necessary
  • btrfs scrub start -rdB /dev/cache → tests and reports without making changes

--- work in progress ---

reiserfsck​

For a full description, please see the About.com page for reiserfsck.

Description​

The reiserfsck tool checks for a Reiser file system (must be a partition like /dev/md3 or /dev/sdc1, not a drive like /dev/sdc), replays any transactions, and checks or repairs it.

Syntax examples​

The filesystem to be repaired must be unmounted. For Unraid, start the array in Maintenance mode.

Note: in the following examples, the option is preceded by 2 hyphens. Drive 3 (/dev/md3) is just used as an example. If you were testing Disk 13, you would use /dev/md13.

  • reiserfsck \--check /dev/md3 → checks file system for errors
  • reiserfsck \--fix-fixable /dev/md3 → fixes file system errors
  • reiserfsck \--rebuild-tree /dev/md3 → rebuilds the file system (may have lost files)
  • reiserfsck \--rebuild-tree -S /dev/md3 → rebuilds the file system from entire partition (may have lost files, may recover old deleted files or their pieces)
  • reiserfsck \--rebuild-sb /dev/md3 → rebuilds superblock based on series of questions, answers MUST be accurate! Please see the Rebuilding the superblock section below.

--- work in progress ---

Rebuilding the superblock​
  • This is an example of the questions and correct answers, when you attempt to rebuild a ReiserFS superblock, using the --rebuild-sb option. The answers MUST be accurate, or the file system may be damaged even more!
  • The example below uses Disk 6 (/dev/md6), so you need to change that to the correct drive symbol for your drive.
  • It is assumed that you have followed the instruction above, and the filesystem to be repaired is unmounted, the array is started in Maintenance mode.
  • The answers you should give are in bold below. Some of the numbers reported will be different for your file system. The UUID will be different too.
  • This is based on the experiences of two users, found here and here. We recommend you read both, for more details.
  • You may want to print this out ahead of time.
       root@Tower:\~# reiserfsck --rebuild-sb /dev/md6
       reiserfsck 3.6.19 (2003 www.namesys.com)

       *************************************************************
       ** If you are using the latest reiserfsprogs and it fails **
       ** please email bug reports to [email protected], **
       ** providing as much information as possible -- your **
       ** hardware, kernel, patches, settings, all reiserfsck **
       ** messages (including version), the reiserfsck logfile, **
       ** check the syslog file for any related information. **
       ** If you would like advice on using this program, support **
       ** is available for $25 at www.namesys.com/support.html. **
       *************************************************************
       Will check superblock and rebuild it if needed
       Will put log info to 'stdout'

       Do you want to run this program?[N/Yes] (note need to type Yes
       if you do):**Yes**

       reiserfs_open: the reiserfs superblock cannot be found on
       /dev/md6.

       what the version of ReiserFS do you use[1-4]
           (1) 3.6.x
           (2) >=3.5.9 (introduced in the middle of 1999) (if you use linux 2.2, choose this one)
           (3) < 3.5.9 converted to new format (don't choose if unsure)
           (4) < 3.5.9 (this is very old format, don't choose if unsure)
           (X) exit
       **1**

       Enter block size [4096]:
       **4096**

       No journal device was specified. (If journal is not available,
       re-run with \--no-journal-available option specified).
       Is journal default? (y/n)[y]: **y**

       Did you use resizer(y/n)[n]: **n**
       rebuild-sb: no uuid found, a new uuid was generated
        (b0894fe9-3850-4d57-b70b-a419cbf3823e)

       rebuild-sb: You either have a corrupted journal or have just
       changed the start of the partition with some partition table
       editor. If you are sure that the start of the partition is ok,
       rebuild the journal header.
       Do you want to rebuild the journal header? (y/n)[n]: **y**
       Reiserfs super block in block 16 on 0x906 of format 3.6 with
       standard journal
       Count of blocks on the device: 97677824
       Number of bitmaps: 2981
       Blocksize: 4096
       Free blocks (count of blocks - used [journal, bitmaps, data,
       reserved] blocks): 0
       Root block: 0
       Filesystem is NOT clean
       Tree height: 0
       Hash function used to sort names: not set
       Objectid map size 0, max 972
       Journal parameters:
           Device [0x0]
           Magic [0x0]
           Size 8193 blocks (including 1 for journal header) (first block 18)
           Max transaction length 1024 blocks
           Max batch size 900 blocks
           Max commit age 30
       Blocks reserved by journal: 0
       Fs state field: 0x1:
           some corruptions exist.
       sb_version: 2
       inode generation number: 0
       UUID: b0894fe9-3850-4d57-b70b-a419cbf3823e
       LABEL:
       Set flags in SB:
       Is this ok ? (y/n)[n]: **y**

It should be quick. When this completes, hopefully successfully, rerun the reiserfsck --check on the drive, and proceed according to the instructions that it gives you.

--- work in progress ---