Anantha N. Srirama writes:
> Therein lies my dillemma: > > - We know the I/O sub-system is capable of much higher I/O rates > - Under the test setup I've SAS datasets which are lending > themselves to compression. This should manifest itself as lots of read > I/O resulting in much smaller (4x) write I/O due to compression. This > means my read rates should be driven higher to keep the compression. I > don't see this, as I said in my original post I see reads comes in > waves. > > I'm beginning to think my write rates are hitting a a bottleneck in > compression as follows: > > - ZFS issues reads > > - ZFS starts compressing the data before the write and cannot drain > the input buffers fast enough; this results in reads to stop. > > - ZFS completes compression and writes out data at a much smaller > rate due to the smaller compressed data stream. > > I'm not a filesystem wizard but shouldn't ZFS take advantage of my > available CPUs to drain the input buffer faster (parallel)? It is > possible that you've some internal throttles in place to make ZFS a > good citizen in the Solaris landscape; a la algorithms in place to > prevent cache flooding by one host/device in EMC/Hitachi. > > I'll perform some more tests with different datasets and report to the > forum. Now if only I can convince my storage administrator to > provision me raw disks instead of the mirrored disks so I can let ZFS > do the same for me, another battle another day ;-) > > Thanks. > > > This message posted from opensolaris.org > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss Yes, compression runs in the context of a single thread per pool so it seems quite possible that it will cause the behavior you see. The issue is being tracked here: http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6460622 -r _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
