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let's assume that i have a raidz created from three disks (or vdevs).

$ fallocate -l 64m /tmp/one
$ fallocate -l 64m /tmp/two
$ fallocate -l 64m /tmp/three
$ sudo zpool create test raidz /tmp/one /tmp/two /tmp/three
$ sudo zpool status test
  pool: test
 state: ONLINE
  scan: none requested
config:

    NAME            STATE     READ WRITE CKSUM
    test            ONLINE       0     0     0
      raidz1-0      ONLINE       0     0     0
        /tmp/one    ONLINE       0     0     0
        /tmp/two    ONLINE       0     0     0
        /tmp/three  ONLINE       0     0     0

errors: No known data errors

for the purpose of increasing the size of the pool, lets say that i have a set of 5 other disks - and i wanted to stripe the two together:

$ fallocate -l 64m four
$ fallocate -l 64m five
$ fallocate -l 64m six
$ fallocate -l 64m seven
$ fallocate -l 64m eight
$ sudo zpool add test raidz /tmp/four /tmp/five /tmp/six /tmp/seven /tmp/eight
invalid vdev specification
use '-f' to override the following errors:
mismatched replication level: pool uses 3-way raidz and new vdev uses 5-way raidz

hmm... so i can force it with -f:

$ sudo zpool add -f test raidz /tmp/four /tmp/five /tmp/six /tmp/seven /tmp/eight
$ sudo zpool status test
  pool: test
 state: ONLINE
  scan: none requested
config:

    NAME            STATE     READ WRITE CKSUM
    test            ONLINE       0     0     0
      raidz1-0      ONLINE       0     0     0
        /tmp/one    ONLINE       0     0     0
        /tmp/two    ONLINE       0     0     0
        /tmp/three  ONLINE       0     0     0
      raidz1-1      ONLINE       0     0     0
        /tmp/four   ONLINE       0     0     0
        /tmp/five   ONLINE       0     0     0
        /tmp/six    ONLINE       0     0     0
        /tmp/seven  ONLINE       0     0     0
        /tmp/eight  ONLINE       0     0     0

and everything 'looks' good...

why do i need to force it? what issues may i run into using this in production?

share|improve this question
    
Use mirrors and you won't have to play these tricks for expansion. –  ewwhite Jul 12 '13 at 9:31
    
except i'll loose 50% capacity on the mirrors... whilst on 33% on 2+1 or 20% on 4+1. –  yee379 Jul 12 '13 at 9:50
    
But you will at least have a scalable path for expansion. –  ewwhite Jul 12 '13 at 10:00
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