Michael Renner <[EMAIL PROTECTED]> writes: > I think your numbers are a bit off: > > For "Consumer drives" (7.200 RPM SATA 3.5"), seek times are much worse, in the > area of 8-9ms (see [1]), but sustained sequential read numbers are noticeable > higher, around 80-90MB/sec.
I took the seek latency from the data sheet for a Barracuda 7200.9 which is several generations old but still a current model. Just rotational latency would have a worst case of 8.3ms and half that is precisely the 4.16 they quote so I suspect that's where the number comes from. Not especially helpful perhaps. They don't quote sustained bandwidth for consumer drives but 50-60MB/s are the numbers I remembered -- admittedly from more than a couple years ago. I didn't realize 7200 RPM drives had reached such speeds yet. But with your numbers things look even weirder. With a 90MB/s sequential speed (91us) and 9ms seek latency that would be a random_page_cost of nearly 100! > For "Server Drives" 3-4ms are more realistic ([2], [3]) for average seeks and > the 110-170MB/sec are highly exaggerated. In that case both of those numbers come straight from Seagate's data sheet for their top-of-the-line data centre drives: http://www.seagate.com/docs/pdf/datasheet/disc/ds_cheetah_15k_6.pdf -- Gregory Stark EnterpriseDB http://www.enterprisedb.com Ask me about EnterpriseDB's Slony Replication support! -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
