Correct way to increase the capacity of an existing pool

TrueNAS General
1

I have a pool that was originally set up with a mirror of 2 HDs each 2TB. One of the disks failed and I replaced it with 8TB disk. The way I replaced it was:

  1. Mark the bad disk as offline.
  2. Physically attached the new 8TB disk
  3. Assign the 8TB disk to the existing pool
    The pool is still 2TB in capacity after resilvering.

Now I just bought another 8TB disk hoping to replace the remaining 2TB disk, with the end result of an 8TB pool utilizing all the disk space on the 2 mirrored drives.

The questions I have:

  1. There is a “Replace” button on the UI. Should I use that instead of the “detach” etc steps?
  2. There is also an “Expand” button next to my existing pool. Does it have any role in my end result, e.g. should I first “replace” 2TB disk with 8TB, then click “Expand”, or does Truenas scale do the expanding automatically?

Based on other people’s comments previously, I think Truenas should automatically increase the capacity of the pool once I replace the 2TB disk with 8TB, but I am unsure what does the “Expand” button do.

2

It does it automatically.

The “Expand” button is sort of a relic of the past, before the default “autoexpand” feature was set on pools.

Don’t use “detach” for this.[1] Either “offline” → “replace” (if you require a reboot and physical swapping of drives), or just skip to “replace” if you have the available slots in your case to house all the drives.

  1. “Detach” will downgrade the mirror vdev to a single disk stripe. ↩︎

2 Likes
3

OK. I just replaced the 1.5TB disk with 8TB.
I first marked the 1.5TB disk as offline.
Powered off the machine, and connected the cables to the 8TB new disk.
Then start TrueNas, and clicked “Replace” on the offline disk, and selected the new 8TB.
After the resilvering, the pool still shows 1.5TB capacity.

There does not seem to be an automatic increase of capacity after.

Did I do something wrong? Do I click Expand button now to get the full 8TB capacity?

01
012523Ă—631 152 KB

02
021234Ă—879 66.9 KB

03
032099Ă—633 135 KB

4

OK, I just tried “Expand” and it increased the pool capacity to 8TB.

I don’t know what I did wrong but there was no automatic expanding of pool capacity after I replaced the remaining smaller disk

04
042481Ă—633 158 KB

with a large one.

5

That is odd.

What does this show:

zpool get autoexpand Photos
6

05
05890Ă—147 5.6 KB

7

Now I’m more confused. By all means, it should have expanded the capacity automatically upon replacing the last drive.

8

autoexpand has been set by default since forever, but apparently iX has forgotten how to partition a disk to use all its space when doing a replacement. This bug has persisted through several versions of SCALE now, and they’ve (falsely) said it’s been fixed at least a few times. I thought it was fixed in 24.10, but perhaps not.

2 Likes
9

Wait. Are you saying this is SCALE-specific bug and doesn’t happen on CORE?

10

Absolutely! Autoexpand-failure is an exclusive SCALE feature.

1 Like
11

AFAIK, no version of CORE is affected by this longstanding SCALE failure.