I don't believe that iozone does any synchronous calls (fsync/O_DSYNC/O_SYNC), so the ZIL and separate logs (slogs) would be unused.
I'd recommend performance testing by configuring filebench to do synchronous writes: http://opensolaris.org/os/community/performance/filebench/ Neil. On 01/15/09 00:36, Gray Carper wrote: > Hey, all! > > Using iozone (with the sequential read, sequential write, random read, > and random write categories), on a Sun X4240 system running OpenSolaris > b104 (NexentaStor 1.1.2, actually), we recently ran a number of relative > performance tests using a few ZIL and L2ARC configurations (meant to try > and uncover which configuration would be the best choice). I'd like to > share the highlights with you all (without bogging you down with raw > data) to see if anything strikes you. > > Our first (baseline) test used a ZFS pool which had a self-contained ZIL > and L2ARC (i.e. not moved to other devices, the default configuration). > Note that this system had both SSDs and SAS drive attached to the > controller, but only the SAS drives were in use. > > In the second test, we rebuilt the ZFS pool with the ZIL on a 32GB SSD > and the L2ARC on four 146GB SAS drives. Random reads were significantly > worse than the baseline, but all other categories were slightly better. > > In the third test, we rebuilt the ZFS pool with the ZIL on a 32GB SSD > and the L2ARC on four 80GB SSDs. Sequential reads were better than the > baseline, but all other categories were worse. > > In the fourth test, we rebuilt the ZFS pool with no separate ZIL, but > with the L2ARC on four 146GB SAS drives. Random reads were significantly > worse than the baseline and all other categories were about the same as > the baseline. > > As you can imagine, we were disappointed. None of those configurations > resulted in any significant improvements, and all of the configurations > resulted in at least one category being worse. This was very much not > what we expected. > > For the sake of sanity checking, we decided to run the baseline case > again (ZFS pool which had a self-contained ZIL and L2ARC), but this time > remove the SSDs completely from the box. Amazingly, the simple presence > of the SSDs seemed to be a negative influence - the new SSD-free test > showed improvement in every single category when compared to the > original baseline test. > > So, this has lead us to the conclusion that we shouldn't be mixing SSDs > with SAS drives on the same controller (at least, not the controller we > have in this box). Has anyone else seen problems like this before that > might validate that conclusion? If so, we think we should probably build > an SSD JBOD, hook it up to the box, and re-run the tests. This leads us > to another question: Does anyone have any recommendations for > SSD-performant controllers that have great OpenSolaris driver support? > > Thanks! > -Gray > -- > Gray Carper > MSIS Technical Services > University of Michigan Medical School > gcar...@umich.edu <mailto:gcar...@umich.edu> | skype: graycarper | > 734.418.8506 > http://www.umms.med.umich.edu/msis/ > > > ------------------------------------------------------------------------ > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
