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I read the specs for one of the latest Hitachi HDD, https://www.hgst.com/sites/default/files/resources/USC10K1800_ds.pdf . It indicates a speed of

SAS 12 Gb/s

which is 1.5 GB/s. Is it the sequential read speed for this HDD? seems to be a lot. If not, what is the sequential read speed for this kind of HDD?

What is also IOPS 100%R / 100%W ?

kiriloff
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1 Answers1

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SAS 12 Gb/s

which is 1.5 GB/s. Is it the sequential read speed for this HDD? seems to be a lot.

12 Gb/s is the SAS interconnect speed, which has little to no bearing on how fast the disk can actually read data off of its platters.

If not, what is the sequential read speed for this kind of HDD?

This depends your use case - what filesystem you're using, how it's configured, what block size the disk is formatted with, etc.

Like with all capacity planning topics, you'll need to profile the drive with your data, and your expected use pattern to get useful data.

What is also IOPS 100%R / 100%W ?

R = Read, W = Write.

You can't have both 100% read & 100% write. Those two percentages need to add up to 100%. When performing drive benchmarks, you'll typically see tests at 50R/50W, 80R/20W, etc.

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  • thanks. in most specs, there is an indicative performance for sequential read/write. is it the sustained transfer rate figure in same Hitachi data sheet? what about IOPS (which corresponds to a random access to 4kb data files)? – kiriloff Nov 11 '15 at 15:12
  • Yes, sequential read/write is equivalent to sustained transfer rate. I'm not sure what you mean by "what about IOPS" -- that *is* random access. The available IOPS of a drive is usually about the reciprocal of seek time. – womble Nov 11 '15 at 23:05