On Fri, Sep 25, 2009 at 5:47 PM, Marion Hakanson <hakan...@ohsu.edu> wrote: > j...@jamver.id.au said: >> For a predominantly NFS server purpose, it really looks like a case of the >> slog has to outperform your main pool for continuous write speed as well as >> an instant response time as the primary criterion. Which might as well be a >> fast (or group of fast) SSDs or 15kRPM drives with some NVRAM in front of >> them. > > I wonder if you ran Richard Elling's "zilstat" while running your > workload. That should tell you how much ZIL bandwidth is needed, > and it would be interesting to see if its stats match with your > other measurements of slog-device traffic.
Yes, but if it's on NFS you can just figure out the workload in MB/s and use that as a rough guideline. Problem is most SSD manufactures list sustained throughput with large IO sizes, say 4MB, and not 128K, so it is tricky buying a good SSD that can handle the throughput. > I did some filebench and "tar extract over NFS" tests of J4400 (500GB, > 7200RPM SATA drives), with and without slog, where slog was using the > internal 2.5" 10kRPM SAS drives in an X4150. These drives were behind > the standard Sun/Adaptec internal RAID controller, 256MB battery-backed > cache memory, all on Solaris-10U7. > > We saw slight differences on filebench oltp profile, and a huge speedup > for the "tar extract over NFS" tests with the slog present. Granted, the > latter was with only one NFS client, so likely did not fill NVRAM. Pretty > good results for a poor-person's slog, though: > http://acc.ohsu.edu/~hakansom/j4400_bench.html I did a smiliar test with a 512MB BBU controller and saw no difference with or without the SSD slog, so I didn't end up using it. Does your BBU controller ignore the ZFS flushes? > Just as an aside, and based on my experience as a user/admin of various > NFS-server vendors, the old Prestoserve cards, and NetApp filers, seem > to get very good improvements with relatively small amounts of NVRAM > (128K, 1MB, 256MB, etc.). None of the filers I've seen have ever had > tens of GB of NVRAM. They don't hold on to the cache for a long time, just as long as it takes to write it all to disk. -Ross _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
