Greg Mason writes:
> We're running into a performance problem with ZFS over NFS. When working
> with many small files (i.e. unpacking a tar file with source code), a
> Thor (over NFS) is about 4 times slower than our aging existing storage
> solution, which isn't exactly speedy to begin with (17 minutes versus 3
> minutes).
>
> We took a rough stab in the dark, and started to examine whether or not
> it was the ZIL.
>
> Performing IO tests locally on the Thor shows no real IO problems, but
> running IO tests over NFS, specifically, with many smaller files we see
> a significant performance hit.
>
> Just to rule in or out the ZIL as a factor, we disabled it, and ran the
> test again. It completed in just under a minute, around 3 times faster
> than our existing storage. This was more like it!
>
> Are there any tunables for the ZIL to try to speed things up? Or would
> it be best to look into using a high-speed SSD for the log device?
>
> And, yes, I already know that turning off the ZIL is a Really Bad Idea.
> We do, however, need to provide our users with a certain level of
> performance, and what we've got with the ZIL on the pool is completely
> unacceptable.
>
> Thanks for any pointers you may have...
>
I think you found out for the replies, this NFS issue is not
related to ZFS nor a ZIL malfunction in any way.
http://blogs.sun.com/roch/entry/nfs_and_zfs_a_fine
NFS (particularly lightly threaded load) is much speeded up
with any form of SSD|NVRAM storage and that's independant on
the backing filesystem used (provided the Filesystem is safe).
For ZFS the best way to acheive NFS performance for lightly
threaded loads is to have a separate intent log in a low
latency device such as in the 7000 line.
-r
> --
>
> Greg Mason
> Systems Administrator
> Michigan State University
> High Performance Computing Center
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