David Magda wrote: > On Wed, June 16, 2010 03:03, Arne Jansen wrote: >> Christopher George wrote: >> >>> For the record, not all SSDs "ignore cache flushes". There are at least >>> two SSDs sold today that guarantee synchronous write semantics; the >>> Sun/Oracle LogZilla and the DDRdrive X1. Also, I believe it is more >> LogZilla? Are these those STEC-thingies? For the price of those I can >> buy a battery backed-up RAID-controller and a few conventional drives. >> For ZIL this will probably do better at a lower price than STEC. > > I'm not sure you'd get the same latency and IOps with disk that you can > with a good SSD: > > http://blogs.sun.com/brendan/entry/slog_screenshots > > You're also talking about using more power (and cooling), and more moving > parts, which can affect reliability numbers. TANSTAAFL. > > Towards the bottom of that post Brendan Gregg configures eight Logzillas > (which I'm sure has the cost of a small car), and got 114,000 synchronous > write ops/sec over NFS; 85% of which were done in under 1.21 ms. I'm not > sure how many spindles you'd need to purchase to get numbers like that in > a more "traditional" configuration.
Please keep in mind I'm talking about a usage as ZIL, not as L2ARC or main pool. Because ZIL issues nearly sequential writes, due to the NVRAM-protection of the RAID-controller the disk can leave the write cache enabled. This means the disk can write essentially with full speed, meaning 150MB/s for a 15k drive. 114000 4k writes/s are 456MB/s, so 3 spindles should do. --Arne _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
