> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of P-O Yliniemi > > Drives for storage: 16*1.5TB Seagate ST31500341AS, connected to two > AOC-SAT2-MV8 controllers > Drives for operating system: 2*80GB Intel X25-M (mirror) > > Is there any advantages for using a separate log or cache device in > this > case ? >
That's a bummer. A waste of perfectly good SSD drives being used for the OS, which basically never sees a benefit from SSD's. Eh, I don't know. Maybe you're performing lots of random reads on your OS disk, although that seems pretty unlikely. I saw your comment about the pool being faster than the SSD's. Here's what you're missing: Spindle disks are faster than SSD's for serial operations, sustained throughput. SSD's are faster for random operations, smaller latency. When you use a SSD for cache or log, you're attempting to leverage the performance benefits of both types of device. The ZIL is only used for sync writes. And sync writes are naturally very latency sensitive. So if you add a SSD log device for dedicated ZIL, then suddenly you're shifting the work load profile to be more serial operations on the spindle disks, and more random operations on the SSD. That is, assuming you're doing some sync writes. If you aren't doing any sync writes, then a SSD log device does you no good whatsoever, except to waste a drive bay. ;-) _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
