Sunday Nov 23, 2008

Two pools on one drive?

Now I'm committed to ZFS root I'm left with a dilemma. Given the four drives I have in the system and that I have too much data and the drives are of different sizes so raid2Z is not an option even though it would give the greatest protection for the data the next best solution is some form of mirroring. Initially I simply had two pools which offers good redundancy and allows ZFS root to work but is suboptimal performance. If I could stripe the pool that would be better but then that does not work with ZFS root.

However since I used to run with a future proof Disk Suite, UFS based root I still have the space that used to contain the two boot environments that were on UFS into which I intended to grow the pool once they were not needed. What if I did not grow the pool but instead put a second pool on that partition? Then I would have a pool, “rpool” mirrored across part of the disk and then the data pool, “tank” mirrored over the rest of the boot drives and striped across a second mirror consisting of the entire second pair of drives.

Clearly the solution is suboptimal but given the constraints of ZFS root and the hardware I have would this perform better?

I should point out that the system as is does not perform badly, but I don't want to leave performance on the table if I don't have to. I'm not going to rush into this (that is I've not already done it) since growing the pool is a one way operation there being no way to shrink it again although at the moment I am minded to do it.

Comments welcome

Saturday Nov 22, 2008

Forced to upgrade

Build 103 and ZFS root have come to the home server. While I was travelling the system hit bug 6746456 which resulted in the system panicing every time it booted. So I was forced to return to build 100 and have now upgraded to build 103. Live upgrade using UFS would not work at all and since I have the space I've moved over to ZFS root. However the nautilus bug is still in build 103 so I'm either going to have to live with it, which is impossible, disable nautilus completely or work to get the time slider feature disabled until it is usable. Disabling nautilus while irritating is effectively what I have had to do now so could be the medium term solution.

The other news for the home server was the failure of the power supply. So it was good bye to the small Antec case that used to house the server since it did not really save any space a more traditional desk side unit has replaced it which also allows upto six internal drives. Since ZFS root will not support booting of stripes the extra two drives I have form a second pool.

# zpool list
NAME    SIZE   USED  AVAIL    CAP  HEALTH  ALTROOT
pool2   294G  36.8G   257G    12%  ONLINE  -
tank    556G   307G   249G    55%  ONLINE  -
# 

The immediate effect of two pools is being able to have the Solaris image from which I upgraded on a different pair of disks from the ones being upgraded with a dramatic performance boost. The other is that I can let the automatic snapshot service take control of the other pool rather than add it to my old snapshot policy. Early on I realise I need to turn off snapshots on the swap volumes which are on both pools (to get some striping):

# zfs set com.sun:auto-snapshot=false pool2/swap
# 
zfs set com.sun:auto-snapshot=false tank/swap 
# 

should do it.

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This is the old blog of Chris Gerhard. It has mostly moved to http://chrisgerhard.wordpress.com

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