ZFS Parity logic in a raidz-2 pool made of different HDD sizes and recommend setup

boris_net

Member

Thanks: 3
Messages: 86

#1
Hi all,

I have the following setup on a backup server I have not looked into for a while:
2 x 4TB
2 x 2TB
13 x 1TB
currently in raidz2 giving me 11TB usable (I did not notice till now but it does not look like the 25TB of capacity going down to 11TB makes a lot of sense).
Can somebody confirm how I end up with 11TB of usable space or in other words, how is the parity calculated with disks of different sizes?

As I have added 2 x 8TB to the system, I am now looking at how to maximize the usable space in either raidz1 or raidz2 and would welcome recommendation on doing so. I can wipe the system that is no issue.

Current pool:
Code:
 pool: zstuff
 state: ONLINE
  scan: scrub repaired 0 in 7h35m with 0 errors on Tue Mar 31 08:00:00 2015
config:

    NAME         STATE     READ WRITE CKSUM
    zstuff       ONLINE       0     0     0
      raidz2-0   ONLINE       0     0     0
        ada0p1   ONLINE       0     0     0
        ada1p1   ONLINE       0     0     0
        ada2p1   ONLINE       0     0     0
        ada3p1   ONLINE       0     0     0
        ada5p1   ONLINE       0     0     0
        ada7p1   ONLINE       0     0     0
        ada8p1   ONLINE       0     0     0
        ada9p1   ONLINE       0     0     0
        ada11p1  ONLINE       0     0     0
        ada12p1  ONLINE       0     0     0
        ada13p1  ONLINE       0     0     0
        ada14p1  ONLINE       0     0     0
        ada15p1  ONLINE       0     0     0
        ada16p1  ONLINE       0     0     0
        ada18p1  ONLINE       0     0     0
And the drives in the system, note: ada4 and ada10 are the new 8TB.

Code:
ada0: 3815447MB (7814037168 512 byte sectors)
ada1: 3815447MB (7814037168 512 byte sectors)
ada2: 953869MB (1953525168 512 byte sectors)
ada3: 953869MB (1953525168 512 byte sectors)
ada4: 7630885MB (15628053168 512 byte sectors)
ada5: 953869MB (1953525168 512 byte sectors)
ada6: 953869MB (1953525168 512 byte sectors)
ada7: 953869MB (1953525168 512 byte sectors)
ada8: 2861588MB (5860533168 512 byte sectors)
ada9: 953869MB (1953525168 512 byte sectors)
ada10: 7630885MB (15628053168 512 byte sectors)
ada11: 953869MB (1953525168 512 byte sectors)
ada12: 953869MB (1953525168 512 byte sectors)
ada13: 953869MB (1953525168 512 byte sectors)
ada14: 953869MB (1953525168 512 byte sectors)
ada15: 953869MB (1953525168 512 byte sectors)
ada16: 953869MB (1953525168 512 byte sectors)
ada17: 953869MB (1953525168 512 byte sectors)
ada18: 2861588MB (5860533168 512 byte sectors)
ada19: 57231MB (117210240 512 byte sectors)
 

phoenix

Administrator
Staff member
Administrator
Moderator

Thanks: 1,177
Messages: 4,017

#2
The smallest member of a vdev sets the size for all members of a vdev, as all members need to be the same size to be usable. Which means only 1 TB of each disk is used to create the vdev. The rest is unused.
 
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