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Can mechanical hard drives (HDD) handle SAS 3's 12GB/s throughput? I'm trying to make a cost analysis that requires maximized transfer speeds but can ONLY use HDD (please don't mention SSDs). Maybe I'm misunderstanding the concept of data transfer falling under the category of reading or writing actions. Even if we purchase 15k RPM, will it make use of SAS3? If not, we'll default to SAS 6 GB/s.
Simonhawk
Posted 2019-03-11T02:46:08.487
Reputation: 21
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It wasn't a typo on my part. SAS/SATA speeds are usually stated in Gigabit per second rather than Gigabyte per second. Further more, as stated, you'd have to look at what you actually want to do and the relevant data sheets.
For instance you might find that an individual HDD only supports a data rate of 0.5 GB/s while reading. That would saturate a 12 Gb/s SAS3 link to ~33%.
But what does the actual use case look like? What does the access pattern of the applications using that drive look like and do you only have a single drive per channel? Define your scenario and afterwards figure out what would satisfy your needs rather than trying to do it the other way around.
Seth
Posted 2019-03-11T02:46:08.487
Reputation: 7 657
Have a look at the datasheet of drives you're interested in. Keep in mind that one might stand MB/s while SAS is Gb/s. So you need to adjust the numbers (12 Gb/s/8 = 1.5 GB/s). Also have a look at the controllers you're interested in and how many individual channels they got (not necessarily the number of connectors). – Seth – 2019-03-11T06:31:05.083
Thanks for the answer. The "Gb/s" was a typo on my part so I apologize for the confusion. I'll take a look at the data sheet to see if I can find anything relevant. Thanks for your input but I'm speaking more from a general perspective. I just wanted to know if the HDD is receiving data at max capacity (12GB/s), will the HDD write or be throttled. The drive might be SAS 3 capable, but it could just be marketing because the drive itself can't handle the speeds. Or is this confusion on my part on the SAS 3 protocol, how data is transferred, and written/read. – Simonhawk – 2019-03-11T11:55:56.513