Constantin Gonzalez wrote: > Hi, > > On a busy NFS server, performance tends to be very modest for large amounts > of small files due to the well known effects of ZFS and ZIL honoring the > NFS COMMIT operation[1]. > > For the mature sysadmin who knows what (s)he does, there are three > possibilities: > > 1. Live with it. Hard, if you see 10x less performance than could be and your > users complain a lot. > > 2. Use a flash disk for a ZIL, a slog. Can add considerable extra cost, > especially if you're using an X4500/X4540 and can't swap out fast SAS > drives for cheap SATA drives to free the budget for flash ZIL drives.[2] >
It is more important to use a separate disk, than to use a separate and fast disk. Anecdotal evidence suggests that using a USB hard disk works well. Remember, slogs are a write-only workload and tend to use very modest amounts of data -- you should see very few seeks on a dedicated slog device. Personally, I'd use a slice from the boot disk, because people tend to leave tons of available space there. -- richard > 3. Disable ZIL[1]. This is of course evil, but one customer pointed out to me > that if a tar xvf were writing locally to a ZFS file system, the writes > wouldn't be synchronous either, so there's no point in forcing NFS users > to having a better availability experience at the expense of performance. > > > So, if the sysadmin draws the informed and conscious conclusion that (s)he > doesn't want to honor NFS COMMIT operations, what are options less disruptive > than disabling ZIL completely? > > - I checked the NFS tunables from: > http://dlc.sun.com/osol/docs/content/SOLTUNEPARAMREF/chapter3-1.html > But could not find a tunable that would disable COMMIT honoring. > Is there already an RFE asking for a share option that disable's the > translation of COMMIT to synchronous writes? > > - The ZIL exists on a per filesystem basis in ZFS. Is there an RFE already > that asks for the ability to disable the ZIL on a per filesystem basis? > > Once Admins start to disable the ZIL for whole pools because the extra > performance is too tempting, wouldn't it be the lesser evil to let them > disable it on a per filesystem basis? > > Comments? > > > Cheers, > Constantin > > [1]: http://blogs.sun.com/roch/entry/nfs_and_zfs_a_fine > [2]: http://blogs.sun.com/perrin/entry/slog_blog_or_blogging_on > > _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
