Zpool with 3 2-way mirrors in a pool


 
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Operating Systems Solaris Zpool with 3 2-way mirrors in a pool
# 1  
Old 08-01-2017
Zpool with 3 2-way mirrors in a pool

I have a single zpool with 3 2-way mirrors ( 3 x 2 way vdevs) it has a degraded disk in mirror-2, I know I can suffer a single drive failure, but looking at this how many drive failures can this suffer before it is no good? On the face of it, I thought that I could lose a further 2 drives in each pool, or even 5, but then I read that if any vdev completely fails in any zpool the entire pool is toast.

Code:
pool1 DEGRADED 
mirror-0 ONLINE
c0t5000C5004835382300 ONLINE
c0t5000CCA02533A897d0 ONLINE
mirror-1 ONLINE 
c0t5000CCA03CA35A25d0 ONLINE
c0t5000C5004867DF01d0 ONLINE
mirror-2 DEGRADED
c0t5000CCA06E11B840d0 ONLINE
c0t5000C5004821F08Fd0 UNAVAIL


Moderator's Comments:
Mod Comment Please use CODE tags as required by forum rules!

Last edited by RudiC; 08-01-2017 at 02:12 PM.. Reason: Added CODE tags.
# 2  
Old 08-01-2017
Your pool can still support two additional disk failures, assuming they are all parts of different mirrors. However, if you lose the second disk of mirror-2, or any pair of disks from the same mirror, your pool is lost and you need to recover from backup.
# 3  
Old 08-02-2017
Thanks for the reply, I now understand.

If I lose another disk in vdev mirror-2, then it's gone.

I guess what I don't fully understand is how the read/write process works across the pool.

For example, a read/write process goes off to pool1, what determines how the data is written across the 3 vdevs I have? Does it just spread it across the 3 vdevs?
# 4  
Old 08-02-2017
ZFS is striping data on the top three vdevs.

There is way to guess which one it will select for a given single record write but on average, writes will be balanced on all devices.
# 5  
Old 08-03-2017
I thought as much, just didn't know for sure!

Thank you for sharing your knowledge.
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