Thanks Richard & Edward for the additional contributions. I had assumed that "maximum sequential transfer rates" on datasheets (btw - those are the same for differing capacity seagate's) were based on large block sizes and a ZFS 4kB recordsize* would mean much lower IOPS. e.g. Seagate Constellations are around 75-141MB/s(inner-outer) and 75MB/s is 18750 4kB IOPS! However I've just tested** a slow 1TB 7200 drive and got over 6000 4kB seq write IOPS which is a lot more than the 500 I was working on.
If this is correct then even with hardly any spindles, if there's enough free space for ZFS to do sequential writes (no interrupting reads etc), you should easily get >6000 4k write IOPS from the disks (ie SLOG IOPS/latency will become limiting factor for sync writes) However, is this what people are actually seeing? (links to any other good reference builds with benchmarks welcome). The "benchmarks" I've found so far are: 1) http://www.zfsbuild.com/2010/10/09/nexenta-core-platform-benchmarks/ (maxed around 4000 write IOPS but iSCSI(sync) to X25-E so could be limited by that - rated 3300 IOPS) 2) http://www.opensolaris.org/jive/thread.jspa?messageID=507090񻳒 One response quoted achieving 550-600 write IOPS on 15k drives (actually just realised this is your response Edward) (if your traffic is large blocks this may explain "lower" iops if bandwidth limited?). ps. Regarding workload and Random reads/L2ARC: The VMs are Windows Servers (Web servers, Databases etc) so the overall mix is random but I'm expecting L2ARC should end up holding frequently read blocks like those behind regularly read database blocks and, especially if we got dedupe working, the Operating System blocks. I also theorise that with thick vmdk files's and defrag'd guest OS and applications, ZFS read-ahead should start to kick in when sequential reads are made to files within the OS. * VMWare over NFS scenario (similar to local database - 4/8kB read/writes to large file) ** IOMeter, 4kB 100% seq, 1 & 64 outstanding, Win7 partition 4kb "alloc unit", Drive write cache enabled (I believe ZFS uses drive write cache) on WD10EACS ). . -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
