On Mar 8, 2010, at 5:11 AM, Edward Ned Harvey wrote: >> It all depends on how they are connecting to the storage. iSCSI, CIFS, >> NFS, >> database, rsync, ...? >> >> The reason I say this is because ZFS will coalesce writes, so just >> looking at >> iostat data (ops versus size) will not be appropriate. You need to >> look at the >> data flowing between ZFS and the users. fsstat works for file systems, >> but >> won't work for zvols, as an example. >> -- richard > > Actually, maybe that is right. Since the users are connecting via CIFS and > NFS and ssh to use a ZFS volume, it stands to reason that ZFS is ultimately > the thing which is performing all the read/write operations on the physical > disks, right? So if I use iostat, and I see coalesced data ... I get > statistics on ops and size ... which is truly the real world usage scenario > for my system, right? Thus, when I am trying to optimize my disk > configuration, benchmarking with iozone or whatever, those statistics will > be the best measurement for me to use, when I tell iozone the blocksize it > should test. Right?
Unfortunately, tools like iozone aren't at all like the real world. If they were, then life would be simple and sweet :-). Consider the case where your application can take advantage of the cache for some items and prefetching for others. It is possible that these workloads don't hit the physical disks. In other words, it is rare that an application acts like a 100% cache miss random workload or 100% sequential workload. This is one reason why more complex load generators, like filebench, exist -- a problem that has dogged capacity planners for a long time. But at the end of the day, your real workload will look different. Oh, and add compression and dedup to really spoil your capacity planner's day :-). One thing is sure: YMMV. -- richard ZFS storage and performance consulting at http://www.RichardElling.com ZFS training on deduplication, NexentaStor, and NAS performance http://nexenta-atlanta.eventbrite.com (March 16-18, 2010) _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
