Can someone please explain these HDD benchmarks to me?

[ctark]

Using CrystalDiskMark it gives you 4 different benchmarks. I'm interested in the first three

Sequential

512k

4k

Can someone explain these to me?

 

[sub.mesa]

Sequential: read or write a large file from begin to end; HDDs are very good in this; SSDs are least good in this (but often still twice as fast as HDDs).

512k: something in between; reading lots of files that are 0.5MB in size. Part sequential, part random.

4k: random I/O, this would access simulated tiny files and involve alot of seeking. This is very fast on SSDs, but extremely slow on HDDs; under 1MB/s usually.

4k-32/64: this is the same test as above, but with a high 'queue depth'. Queue depth means multiple requests are being sent at the same time, up to 64 queued I/O's. SSDs are parallel devices and can execute up to 10 I/O's at the same time (10 channels). HDDs are serial devices and wouldn't have that benefit.

So HDDs would only show good scores in the first (sequential) benchmark, and decent results on the 512k benchmark; but the others would suck.

 

[Emulex]

actually some hard drives have two servos. and caching raid scenarios can produce far greater than 10 depth. i was running well past 32 depth 24x7x365 (years) about 15 years ago on a small cheap 586-based scsi san.