On Thu, Apr 16, 2009 at 12:11 PM, Nicholas Lee <emptysa...@gmail.com> wrote:
> > Let me see if I understand this: A SSD slog can handle, say, 5000 (4k) > transactions in a sec (20M/s) vs maybe 300 (4k) iops for a single HDD. The > slog can then batch and dump say 30s worth of transactions - 600M as > one sequential write - say 15s (at 40M/s) for a single HDD. So maybe at most > 2GB is needed for 60s worth of traffic. > > And this is the big win for sync NFS - .2ms latency vs 3+ms latency. For 4k > NFS blocks at 3ms latency difference that is 10,000/4*3/1000 = 7.5 sec of > extra latency for a 10M file. Ignoring all other latency issues. > > Not sure what the iops for a SSD is at 32k. But assuming, 3000 iops at 30k > means 96M/s or 5GB for 60s. So for a 10MB file the latency difference at > 32k is only 1 sec. > Actually my numbers might be a little out: http://www.anandtech.com/cpuchipsets/Intel/showdoc.aspx?i=3403&p=8 For the X25-M (-E is probably better - The X25-M is rate internally limited to 80M/s), the random iops where: - At 4k .089ms or 11.2k iops = 45M/s - At 16k .23ms or 4.3k iops = 69M/s - At 32k .44ms or 2.3k iops = 74M/s - At 64k .84ms or 1.2k iops = 77M/s - At 128k 1.73ms or .6k iops = 77M/s They use a Momentus 7200.2 at 100 iops (regardless of packet size), a better drive would should get 300 iops. Nicholas
_______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
