ZFS sync / ZIL clarification

Johan Hendriks joh.hendriks at gmail.com
Tue Jan 31 20:36:43 UTC 2012


Mark Felder schreef:
> I believe I was told something misleading a few weeks ago and I'd like 
> to have this officially clarified.
>
> NFS on ZFS is horrible unless you have sync = disabled. I was told 
> this was effectively disabling the ZIL, which is of course naughty. 
> Now I stumbled upon this tonight:
Well i did a test from my ESXi 5.0 server.
That server has a local store (2 x 146 GB 15k SAS drives) The ESXi 
server is a HP proliant ML380 with 60 GB mem.

The ZFS server is a supermicro 3U 16 bay storage server, with a zpool 
created with mirrors from all the old disk we have.
this are 80 GB drives, 250 GB drives 750 GB drives, all sata and some of 
them nearly passes smartctl and one is already marked failed :D..
The machines are connected through a simple 8 port HP 1Gb switch.

If i do a copy from the local store to the NFS store, performance is 
bad, well very bad.

Below is the performance graph from the esxi host. During the copy i did 
the zfs set sync=disabled sanstore/ESXishare-bck  command.

http://doub.home.xs4all.nl/bench/sync.png

You see that the speed goes up, not a little, but it almost makes the 
older copy graph invisable.
ESXi + ZFS without sync is disabled is a no go.

regards
Johan Hendriks



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