Hello Jonathan, Tuesday, February 6, 2007, 5:00:07 PM, you wrote:
JE> On Feb 6, 2007, at 06:55, Robert Milkowski wrote: >> Hello zfs-discuss, >> >> It looks like when zfs issues write cache flush commands se3510 >> actually honors it. I do not have right now spare se3510 to be 100% >> sure but comparing nfs/zfs server with se3510 to another nfs/ufs >> server with se3510 with "Periodic Cache Flush Time" set to disable >> or so longer time I can see that cache utilization on nfs/ufs stays >> about 48% while on nfs/zfs it's hardly reaches 20% and every few >> seconds goes down to 0 (I guess every txg_time). >> >> nfs/zfs also has worse performance than nfs/ufs. >> >> Does anybody know how to tell se3510 not to honor write cache flush >> commands? JE> I don't think you can .. DKIOCFLUSHWRITECACHE *should* tell the array JE> to flush the cache. Gauging from the amount of calls that zfs makes to JE> this vs ufs (fsck, lockfs, mount?) - i think you'll see the JE> performance diff, JE> particularly when you hit an NFS COMMIT. (If you don't use vdevs you JE> may see another difference in zfs as the only place you'll hit is on JE> the zil) IMHO it definitely shouldn't actually. The array has two controllers and write cache is mirrored. Also this is not the only host using that array. You can actually win much of a performance, especially with nfs/zfs setup (lot of synchronous ops) I guess. IIRC Bill posted here some tie ago saying the problem with write cache on the arrays is being worked on. JE> btw - you may already know, but you'll also fall to write-through on JE> the cache JE> if your battery charge drops and we also recommend setting to write- JE> through JE> when you only have a single controller since a power event could JE> result in JE> data loss. Of course there's a big performance difference between JE> write-back and write-through cache I can understand reduced performance with one controller (however I can force write-back on se3510 even with one controller - depending on situation we can argue if it would be wise or not) however until write cache is protected I definitely do not want ZFS to issue DKIOCFLUSHWRITECACHE. Ideally ZFS could figure out itself with recognized arrays. But I would like to be able to set it my self on pool basis anyway (there're always specific situations). -- Best regards, Robert mailto:[EMAIL PROTECTED] http://milek.blogspot.com _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
