On Dec 2, 2009, at 6:57 AM, Brian McKerr <br...@datamatters.com.au>
wrote:
Hi all,
I have a home server based on SNV_127 with 8 disks;
2 x 500GB mirrored root pool
6 x 1TB raidz2 data pool
This server performs a few functions;
NFS : for several 'lab' ESX virtual machines
NFS : mythtv storage (videos, music, recordings etc)
Samba : for home directories for all networked PCs
I backup the important data to external USB hdd each day.
I previously had a linux NFS server that I had mounted 'ASYNC' and,
as one would expect, NFS performance was pretty good getting close
to 900gb/s. Now that I have moved to opensolaris, NFS performance
is not very good, I'm guessing mainly due to the 'SYNC' nature of
NFS. I've seen various threads and most point at 2 options;
1. Disable the ZIL
2. Add independent log device/s
I happen to have 2 x 250GB Western Digital RE3 7200rpm (Raid
edition, rated for 24x7 usage etc) hard drives sitting doing nothing
and was wondering whether it might speed up NFS, and possibly
general filesystem usage, by adding these devices as log devices to
the data pool. I understand that an SSD is considered ideal for log
devices but I'm thinking that these 2 drives should at least be
better than having the ZIL 'inside' the zpool.
If adding these devices, should I add them as mirrored or individual
to get some sort of load balancing (according to zpool manpage) and
perhaps a little bit more performance ?
I'm running ZFS version 19 which 'zpool upgrade -v' shows me as
having 'log device removal' support. Can I easily remove these
devices if I find that they have resulted in little/no performance
improvements ?
Any help/tips greatly appreciated.
It wouldn't hurt to try, but I'd be surprised if it helped much if at
all. Idea of a separate ZIL is to locate it on a device with lower
latency then the pool which would help increase performance between
pool and log writes.
What speed are you trying to achieve for writes? Wirespeed? Well it's
achievable, but with an app that uses larger block sizes and allows
more then 1 transaction in flight at a time.
I wouldn't disable the ZIL but look at tuning the client side, or you
could invest in a controller with a large battery backed write-cache
and good JBOD mode, or a small fast SSD drive.
-Ross
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