RAIDz2 mixed disks available storage greater than smallest disks?

TrueNAS General
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1

Hi all, I am a bit confused. I thought that if I have a RAIDz2 with 2x3tb and 2x2tb disks, then (since there is a 2 drive redundancy) I should only have 2tb storage available, but I seem to have 3tb?!? I guess that I can lose the 2x3tb and still have >2tb data on the 2x2tb disks… reading old posts seems to point towards space being the smallest disk, but has this changed?

Ignore the degradation, I am in the process of removing the GELI encryption. according to How to remove encryption from a ZFS volume (while keeping the data) | TrueNAS Community

root@freenas:/ # zfs list maindata
NAME       USED  AVAIL  REFER  MOUNTPOINT
maindata  2.35T  1.06T   360K  /mnt/maindata

root@freenas:/ # zpool list maindata
NAME       SIZE  ALLOC   FREE  CKPOINT  EXPANDSZ   FRAG    CAP  DEDUP    HEALTH  ALTROOT
maindata  7.25T  4.68T  2.57T        -         -    43%    64%  1.00x  DEGRADED  /mnt

root@freenas:/ # zpool status -v maindata
  pool: maindata
 state: DEGRADED
status: One or more devices is currently being resilvered.  The pool will
        continue to function, possibly in a degraded state.
action: Wait for the resilver to complete.
  scan: resilver in progress since Sat Apr 26 06:19:31 2025
        2.99T / 4.68T scanned at 312M/s, 2.22T / 4.66T issued at 232M/s
        555G resilvered, 47.60% done, 03:04:19 to go
config:
        NAME                                                  STATE     READ WRITE CKSUM
        maindata                                              DEGRADED     0     0     0
          raidz2-0                                            DEGRADED     0     0     0
            gptid/85858002-5059-11ec-9c0f-d8d385636e4c.eli    ONLINE       0     0     0
            gptid/16fbe186-df2e-11e6-857a-d8d385636e4c.eli    ONLINE       0     0     0
            replacing-2                                       DEGRADED     0     0     0
              gptid/bf6c6035-95c2-11e5-a2cd-d8d385636e4c.eli  OFFLINE      0     0     0
              gptid/bf6c6035-95c2-11e5-a2cd-d8d385636e4c      ONLINE       0     0     0  (resilvering)
            gptid/c032a980-95c2-11e5-a2cd-d8d385636e4c        ONLINE       0     0     0

errors: No known data errors

root@freenas:/ # geom disk list | egrep "(ada|Mediasize)"
Geom name: ada0
1. Name: ada0
   Mediasize: 3000592982016 (2.7T)
Geom name: ada1
1. Name: ada1
   Mediasize: 3000592982016 (2.7T)
Geom name: ada2
1. Name: ada2
   Mediasize: 2000398934016 (1.8T)
Geom name: ada3
1. Name: ada3
   Mediasize: 2000398934016 (1.8T)
2

You have 4 disks. Using RaidZ2 uses two disks for parity. You have 2 disks worth of space for storage.

The smallest disk size is 2tb, therefore you have 2*2tb = 4tb worth of storage space, essentially

SIZE means total drive capacity available without parity. 4*1.8 = 7.2

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