On 6/26/07, Roshan Perera <[EMAIL PROTECTED]> wrote:
25K 12 CPU dual core x 1800Mhz with ZFS 8TB storage SAN storage (compressed & RaidZ) Solaris 10.
RaidZ is a poor choice for database apps in my opinion; due to the way it handles checksums on raidz stripes, it must read every disk in order to satisfy small reads that traditional raid-5 would only have to read a single disk for. Raid-Z doesn't have the terrible write performance of raid 5, because you can stick small writes together and then do full-stripe writes, but by the same token you must do full-stripe reads, all the time. That's how I understand it, anyways. Thus, raidz is a poor choice for a database application which tends to do a lot of small reads.
Using mirrors (at the zfs level, not the SAN level) would probably help with this. Mirrors each get their own copy of the data, each with its own checksum, so you can read a small block by touching only one disk. What is your vdev setup like right now? 'zpool list', in other words. How wide are your stripes? Is the SAN doing raid-1ish things with the disks, or something else?
2. Unfortunately we are using twice RAID (San level Raid and RaidZ) to overcome the panic problem my previous blog (for which I had good response).
Can you convince the customer to give ZFS a chance to do things its way? Let the SAN export raw disks, and make two- or three-way mirrored vdevs out of them.
3. Any way of monitoring ZFS performance other than iostat ?
In a word, yes. What are you interested in? DTrace or 'zpool iostat' (which reports activity of individual disks within the pool) may prove interesting. Will _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
