On Jun 15, 2006, at 06:23, Roch Bourbonnais - Performance Engineering wrote:
Naively I'd think a write_cache should not help throughput test since the cache should fill up after which you should still be throttled by the physical drain rate. You clearly show that it helps; Anyone knows why/how a cache helps throughput ?
7200 RPM disks are typically IOP bound - so the write cache (which can be up to 16MB on some drives) should be able to buffer enough IO to deliver more efficiently on each IOP and also reduce head seek. Not sure which vendors implement write through when the cache fills, or how detailed the drive cache algos on SATA can go .. Take a look at PSARC 2004/652: http://www.opensolaris.org/os/community/arc/caselog/2004/652/ .je _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
