Re: That table again...
"I would dearly love more accurate numbers."
seek times for drives, these will be performance drives as this table is comparing a new performance storage device to current devices.
An enterprise performance sas drive, including controller overhead, 10k rpm, as no one will really buy 15k anymore.
read seek:
average: 4.2ms
single track: 0.4ms
full stroke: 7.68ms
Write seek:
average: 4.6ms
single track: 0.7ms
full stroke: 8.15ms
rotational latency: 3ms
or if SSD is considered a drive: ~0.1ms
DAS:
Take those same drives, if not taking into account the controller which will no doubt have cache on board for read and writes, add effectively nothing, with cache, reduce it.
SAN:
Same as DAS, if not taking into account of write caching, for spinning, add nothing, SSD is slightly different, can introduce a little more latency. Switching latency for FC is in nanoseconds, for example a brocade 300 will have a maximum latency of 700ns.
Example of performance for a SAN, 3PAR 7200 using 8gb FC, with a flash tier will give around 0.2ms read/write latency, write latency will be lower than read as they will go to cache first, same with 10k drives, write latency will be in the region of 0.1-0.2ms with reads around 5-8ms, and for NL 12-15ms.
Latency will change of course depending upon load, increasing as more requests come in at the same time.
Biting the hand that feeds IT
