On Aug 4, 2009, at 7:26 AM, Joachim Sandvik <no-re...@opensolaris.org>
wrote:
does anybody have some numbers on speed on sata vs 15k sas? Is it
really a big difference?
For random io the number of IOPS is 1000/(mean access + avg rotational
latency) (in ms)
Avg rotational latency is 1/2 the rotational latency which is 1/
(rotations per second), which for 15K = 250 and for 7200 = 120.
This means for 15K drives the arl = 2ms and for 7200 the arl = 4.150ms.
So for each random io take the mean access time add the arl and divide
1000 by that number.
SAS disks tend to have faster access times, so say a top SAS disk has
an access time of 4ms + ARL = 6ms, a top SATA disk has an access time
of 8ms + ARL = 12ms
1000/6 = 167 IOPS for SAS
1000/12 = 83 IOPS for SATA
Then follow the guidelines for how RAIDed disks increase or decrease
the IOPS by the RAID type.
We could also go for a mix of sata and 15K sas on the storage box,
with 10 sata in 1 pool, and 10 sas in another pool.
I recommend SAS for all storage that does primariy random io and SATA
for storage that does primarily sequential io.
-Ross
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
