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Shrink Array

Note: this page has been tested for v6, but is still fairly new.

Why would you want to shrink your array?

  • Maybe you have recently found a red ball on one of your drives, and you want to take it out of the array. You've got enough extra space, and don't need to replace the drive.
  • Or you are consolidating drives, replacing multiple smaller drives with new and larger ones.
  • Or you have an array drive that you no longer want in the array, for whatever reason, and you don't want to replace it.
  • Or you are out of SATA ports, and have emptied a smaller drive so you can remove it, and reuse the SATA port.
  • Or you wish to take one or more data drives to a new or different array, intact with all its data.

In general, the best choice is to replace an unwanted or disabled drive by assigning a replacement drive, and allowing Unraid to rebuild it. This way, parity protection for the array is maintained. The following methods are for those who do not want to replace the drive, and are OK with a temporary loss of parity protection. (There is a method below that preserves parity!) Update: a procedure to remove one or more drives without invalidating parity protection is discussed here. It involves a dangerous command at a command prompt, so command line experience is desirable.

Here are the procedures and methods for shrinking the array without losing any data. Note: these procedures work exactly the same whether your drive is disabled or not.

For Unraid v6.2 and later​

There are 2 methods here for removing drives from an Unraid v6.2 array. Check the conditions and comments at the top of each method, to know which one will work best for your situation.

The "Remove Drives Then Rebuild Parity" Method​

For removing one or more drives from an Unraid array - this is the tried and true method Note: this section has been tested for 6.2, but is still fairly new

  • This method does not keep the drive's data within the array. If the drive to be removed has data you want to stay in the array, you must move it yourself to the other data drives. Parity will be built based entirely and only on the remaining drives and their contents.
  • This method is best if you are removing more than one drive.
  • This method should be used if you need to preserve the contents of the data drive you are removing from the array.
  • This method MUST be used if the drive cannot be cleared, that is, it is missing, disabled, or has bad sectors.
  • This method does NOT preserve parity, so parity will have to be rebuilt once the array assignments have been adjusted.
Procedure​
  1. Make sure that the drive or drives you are removing have been removed from any inclusions or exclusions for all shares, including in the global share settings. Shares should be changed from the default of "All" to "Include". This include list should contain only the drives that will be retained.
  2. Make sure you have a copy of your array assignments, especially the parity drive. You may need this list if the "Retain current configuration" option doesn't work correctly
  3. Stop the array (if it is started)
  4. Go to Tools then New Config
  5. Click on the Retain current configuration box (says None at first), click on the box for All, then click on close
  6. Click on the box for Yes I want to do this, then click Apply then Done
  7. Return to the Main page, and check all assignments. If any are missing, correct them. Unassign the drive(s) you are removing. Double check all of the assignments, especially the parity drive(s)!
  8. Do not click the check box for Parity is already valid; make sure it is NOT checked; parity is not valid now and won't be until the parity build completes
  9. Start the array to commit the changes; system is usable now, but it will take a long time rebuilding parity

The "Clear Drive Then Remove Drive" Method​

For removing a drive from an Unraid array, while maintaining the parity protection - this is a new method Note: this section has been tested but is still fairly new

  • This method preserves parity protection at all times.
  • This method can only be used if it's a good drive that is completely empty, is mounted in the array, and can be completely cleared.
  • This method is limited to removing only one drive at a time.
  • As stated above, the drive must be completely empty. If there are still any files on it (including hidden ones), they must be moved to another drive, or deleted.
  • One quick way to clean a drive is reformat it! To format an array drive, you stop the array and then on the Main page click on the link for the drive and change the file system type to something different than it currently is, then restart the array. You will then be presented with an option to format it. Formatting a drive removes all of its data, and the parity drive is updated accordingly, so the data cannot be easily recovered.
  • Explanatory note: "Since you are going to clear the drive anyway, why do I have to empty it? And what is the purpose of this strangeclear-mefolder?" Yes it seems a bit draconian to require the drive to be empty since we're about to clear and empty it in the script, but we're trying to be absolutely certain we don't cause data loss. In the past, some users misunderstood the procedure, and somehow thought we would preserve their data while clearing the drive! This way, by requiring the user to remove all data, and then add an odd marker, there cannot be any accidents or misunderstandings and data loss.
Procedure​
  1. Make sure that the drive you are removing has been removed from any inclusions or exclusions for all shares, including in the global share settings.
  2. Make sure the array is started, with the drive assigned and mounted.
  3. Make sure you have a copy of your array assignments, especially the parity drive. You may need this list if the "Retain current configuration" option doesn't work correctly.
  4. It is highly recommended to turn on reconstruct write, as the write method (sometimes called 'Turbo write'). With it on, the script can run 2 to 3 times as fast, saving hours! In Settings → Disk Settings, change Tunable (md_write_method) to reconstruct write.
  5. Make sure ALL data has been copied off the drive; drive MUST be completely empty for the clearing script to work.
  6. Double check that there are no files or folders left on the drive. Note: one quick way to clean a drive is reformat it! (once you're sure nothing of importance is left of course!)
  7. Create a single folder on the drive with the name clear-me - exactly 7 lowercase letters and one hyphen
  8. Run the clear an array drive script from the User Scripts plugin (or run it standalone, at a command prompt).
    • If you prepared the drive correctly, it will completely and safely zero out the drive. If you didn't prepare the drive correctly, the script will refuse to run, in order to avoid any chance of data loss.
    • If the script refuses to run, indicating it did not find a marked and empty drive, then very likely there are still files on your drive. Check for hidden files. ALL files must be removed!
    • Clearing takes a loooong time! Progress info will be displayed, in 6.2 or later. Prior to 6.2, nothing will show until it finishes.
    • If running in User Scripts, the browser tab will hang for the entire clearing process.
    • While the script is running, the Main screen may show invalid numbers for the drive, ignore them. Important! Do not try to access the drive, at all!
  9. When the clearing is complete, click done and stop the array - do not remove the cleared disk yet.
  10. Go to Tools then New Config
  11. Click on the Retain current configuration box (says None at first), click on the box for All, then click on close
  12. Click on the box for Yes I want to do this, then click Apply then Done
  13. Return to the Main page, and check all assignments. If any are missing, correct them. Unassign the drive(s) you are removing. Double check all of the assignments, especially the parity drive(s)! If the cleared drive is "hot-swappable" you may now remove the cleared drive and follow the steps below. If it is not, follow the steps below.
  14. Click the check box for Parity is already valid, make sure it is checked!
  15. Start the array! Click the Start button then the Proceed button (on the warning popup that will pop up)
  16. Parity should still be valid, however it's highly recommended to do a Parity Check
  17. If you do not have hot swappable drives, you may now safely shutdown your server and remove the cleared drive.
Alternate Procedure for Linux proficient users​

It's actually the same procedure as above, except that you can replace steps 7 and 8 by performing the clearing commands yourself at a command prompt. (Clearing takes just as long though!) If you would rather do that, than run the script in steps 7 and 8, then here are the 2 commands to perform:

umount /mnt/diskX
dd bs=1M if=/dev/zero of=/dev/mdX status=progress
(where X in both lines is the number of the data drive being removed)

Important!!! It is VITAL you use the correct drive number, or you will wipe clean the wrong drive! That's why using the script is recommended, because it's designed to protect you from accidentally clearing the wrong drive.

For Unraid v6.0 and 6.1 and possibly 5.0​

  • Notice: This section has been partially rewritten, is not well tested yet. But it's based on the old tried and true method for removing drives
  • These instructions assume you are using Unraid v6, but may work for Unraid v5 also.
  • This procedure starts by removing all drive assignments. You will then need to reenter all of them from your notes, making any changes you desire.
Procedure​
  1. Take a screenshot of your current array assignments, or make good notes of them
  2. Make sure that the drive or drives you are removing have been removed from any inclusions or exclusions for all shares, including in the global share settings.
  3. Stop the array (if it is started)
  4. Go to <Tools> and click <New config>, then <Apply>, then <Done>
  5. Reassign all disks except the ones you are removing, using your notes or screen shot
  6. Double check that your Parity disk(s) are assigned correctly!
  7. Do not click the check box for "Parity is already valid"; make sure it is NOT checked; parity is not valid now and won't be until the parity build completes
  8. Start the array - will take a long time while it rebuilds parity
Alternate procedure that maintains parity protection​

  • If you wish, the "Clear Drive Then Remove Drive" method in the 6.2 section above can be carefully adapted for use. You won't have the "Retain" option, or the "reconstruct write" tunable option, or the User Scripts plugin. v5 users may have to use the "Trust Parity" method rather than the "Parity is already valid" option. And you won't have any progress info at all during the clearing! It will be finished when it finishes!

  • *In Unraid v6.0 and v6.1 (not v5), you can turn on "reconstruct write" (sometimes known as "turbo write" because it runs significantly faster) with the following command at the command line *after* the array is started:

    mdcmd set md_write_method 1