Currently running 4-disk raidz1 - Looking for assistance migrating to 8-disk raidz2

[ASchneider]

I've been skating by on a 4-disk raidz1 device for a few years, and recently had a disk die on me, which has led me toward migrating to raidz2 for the extra redundancy. My current zpool has the following configuration of disks:

root@r720-poweredge-1:~# zpool status
  pool: SAS-7.2k
 state: ONLINE
  scan: scrub repaired 0B in 14:26:01 with 0 errors on Sun Feb 11 14:50:13 2024
config:

        NAME                        STATE     READ WRITE CKSUM
        SAS-7.2k                    ONLINE       0     0     0
          raidz1-0                  ONLINE       0     0     0
            wwn-0x5000cca26c2d2d08  ONLINE       0     0     0
            wwn-0x5000cca26a9fe54c  ONLINE       0     0     0
            wwn-0x5000cca26a902198  ONLINE       0     0     0
            wwn-0x5000cca26a99d46c  ONLINE       0     0     0

errors: No known data errors

Each disk is 10TB, and the total storage utilization of that pool is 13.27TB. I have an R720 that I've added an additional four 10TB disks to. My end goal is to have a single raidz2 device consisting of all 8 disks, running under a single zpool. My current issue is that with just under 14TB, I don't have a secondary host that can hold all of that data in the event I need to scrub the old pool prior to forming the new pool.

Is there a way that I can create a raidz2 device under it's own storage pool, losslessly move all of the data from the old pool to the new one, scrub the old pool and wipe the disks, and then add the old disks to the new raidz2 device?

 

[Dunuin]

No, best is still to backup all data to some other storage (replication to another ZFS pool would keep all settings and snapshots and should be fastest), destroy the existing pool and create a new one. That way you also defrag you data.

Only option I could think of would be using the 4 new disks to create an additional 4 disk raidz2 pool. Then replicating data from old to new pool, destroying the old pool and extending the raidz2 pool with the 4 old disks. But this then will result in a 8 disk raidz2 pool that got the bad parity-to-data-ratio of a 4 disk raidz2. So loss of 50% and not the usual 25% loss of raw capacity for your old data. Not a great option unless you then destroy your old data and recreate it (moving all data/blocks between datasets/zvols should work as you also double your free space). But keep in mind that raid and snapshots don't count as backups...you should have enough additional space to properly backup all data you care about anyway...so destroying the pool and starting from scratch shouldn't be a problem in the first place.
Or you drop the idea of a raidz2 and stripe another 4 disk raidz1 to double the capacity and IOPS performance while not increasing the resilvering time.
Or stick with the 4 disk raidz1 and use the 4 new disks to create another 4 disk raidz1 pool to store your backups so you got at least a second copy of everything (and a third copy offsite using another filesystem/media would be highly recommended too if you really care about your data and want to follow the "3-2-1 backup rule").

 

[UdoB]

Slow down, @Dunuin ;-)

Yes, it is coming, but the currently installed version in PVE 8.1.4 tells me it is ZFS 2.2.2 and for this reason:

SYNOPSIS
     zpool attach [-fsw] [-o property=value] pool device new_device
DESCRIPTION
     Attaches new_device to the existing device.  The existing device cannot be part of a raidz configuration.

 

[Dunuin]

Ah ok, thought it got finally added with 2.2. They you have to wait for the feature to be added or recreate the pool from scretch