Hi there!

I want to re-structure my array a bit:

- remove 3-4 old HDDs

- remove the current two Parity disks

- add one new, bigger Parity drive

- (optional) add one BIGGER drive back in

And I want to do that with as little stress on the disks as possible, as you can imagine.

I saw the great Spaceinvader One video on array shrinking the Array and figured: if I go with method 1, could I probably do this in a "single" step? Because I need to rebuild Parity anyway?

The plan would be:

- do a full Array backup(!)

- use unBALANCE to free the disks I want to remove

- shutdown, remove the disks from the server, add in the new Parity, restart

- (optional) put that one bigger drive inside as well

- do the re-structuring-thing

- assign the disks to the Array

- let the Parity rebuild

- (optional) run unBALANCE again to relieve the filling of the old disks to the new one

(probably the new disk shouldn't be added to the Array right away, but pre-cleared when parity is rebuild, and then added)

At least it feels like this could be a viable way, only difference to the video is that I'd remove more drives at once, which shouldn't matter when they're empty and the Parity is rebuild anyway?

Best Regards,

Rick

Personally I would add your second parity drive first and rebuild parity. Remember that both these drives must be larger than any other drive.

After the rebuild is complete add the large array drive. If it’s new and you want to test it you can preclear it. If it’s not new and under warranty you can just let the system clear the drive as part of the “add” process.

After adding the large drive you can move data as required to empty the small drives and remove them.

If you have a large amount of empty space on your array you might possibly combine the removing of the small drives and adding the large one.

1 hour ago, wgstarks said:

Personally I would add your second parity drive first and rebuild parity. Remember that both these drives must be larger than any other drive.

Ah, I wasn't precise enough: currently, I have two Parity drives. I want to switch to just one Parity. The new Parity is going to be larger than the current ones :)

Your idea with adding a new one first and and then emptying the old ones is clever! I have to see how I could possibly do that though, as my case can't physically hold any more drives (but of course, the slot of Parity#2 would be free)
In that case, the removal of the old disks would probably be method 2 from the Video, so I would not have to rebuild the Parity again.

Regarding the pre-clear: as far as I remember, the auto-clear from the system is basically a pre-clear, but during this operation the Parity is under heavy stress as well?

Currently, I have enough free space to remove the three disks (with ~3-4TB buffer). But the more I think about your approach, the more I understand that it would potentially mean less downtime as well, which is pretty dope

Best,

Rick

3 minutes ago, CameraRick said:

the auto-clear from the system is basically a pre-clear, but during this operation the Parity is under heavy stress as well?

The clearing disk isn't added to the array until after it is clear. The clearing operation has no effect on parity, just as the cleared disk has no effect on parity when it is added.

45 minutes ago, trurl said:

The clearing disk isn't added to the array until after it is clear. The clearing operation has no effect on parity, just as the cleared disk has no effect on parity when it is added.

I now wanted to google where my misconception may have come from, only to find a great explanation in a post from you, haha :)

okay, I somehow thought this would either stress Parity or take the array offline, so I won't bother with that. Thanks for clearing that up (two times even, haha)

Best,

Rick

I misread your first post but the basic steps would still be the same.

I would change the parity drives first using “new config” and rebuild parity.

After the rebuild is finished make your changes to the array.

Thanks for the headsup, that indeed sounds good!

For HDDs-got-really-expensive reasons, I think about not directly buying a new Parity bisk, but going down to just one - and put the 2nd one into the Array, and then fishing the three old disks out.

The Documentation makes me believe that I can just unassign one of them, and not rebuild Parity? I probably misread this, right?

Best,

Rick

16 minutes ago, CameraRick said:

Thanks for the headsup, that indeed sounds good!

For HDDs-got-really-expensive reasons, I think about not directly buying a new Parity bisk, but going down to just one - and put the 2nd one into the Array, and then fishing the three old disks out.

The Documentation makes me believe that I can just unassign one of them, and not rebuild Parity? I probably misread this, right?

Best,

Rick

It doesn't actually say that your server won't start a parity rebuild. I've never used 2 parity disks so can't be sure but I would expect it to start a rebuild when you start the array.

Appare

3 hours ago, wgstarks said:

I've never used 2 parity disks so can't be sure but I would expect it to start a rebuild when you start the array.

I did the same, but apparently you don't need to do this, according to this thread (again with great explanations from @trurl , I see a pattern)

Will do this later, then I can start with copying the files real soon :)

The linked documentation for shrinking the array has 2 methods. The 2nd method preserves parity by zeroing the disk to be removed while it is still in the array. This has the effect of updating parity at the same time as the disk to be removed is being zeroed, so at the end, parity agrees the disk is clear so removing it has no further effect on parity. Then it is OK to New Config/Parity Valid and avoid the parity rebuild since parity is already valid without the removed disk.

It is always OK to remove one of the parity disks without rebuilding the other parity disk if you don't change any other assignments.

If you add or remove an array data disk that isn't clear you must rebuild any parity still assigned.

As long as you don't add or remove an array data disk that isn't clear, you can change the slot assignments of the data disks without rebuilding parity, but changing slot assignments requires rebuilding parity2.

Thanks for the great explanations yet again! :)

The two methods of removing an array drive are also in the video (but presented in a way that fits dummies like me a bit better, haha). I linked it because of the Parity2 removal (which was, again, not properly worded by me), which is is now also clear to me; in other videos/forum posts, I also learned about the "copy" method to replace a Parity while simultaneously adding the old Parity disk to the array; cool technique, don't know if I had the guts, haha :)

Either way, I am now rather confident with how to tackle all of this. For now, I will not buy a new drive, but just remove Parity 2. Then add it to the array; after it's in, scatter four* old disks to the remaining ones, and remove those.

Because zero'ing four drives will probably take some time, I will likely just remove them and rebuild Parity (I still have backups if a drive suddenly fails).

* I "need" to strip down to 8drives total, and the earlier plan with three was just a temporary one; with this new game-plan, I can do better, but need to remove one more; I will still get a new Parity later, but postpone that till I get my tax-returns, haha

Best,
Rick