HDDs are OK if your workload consists of long sequential reads or writes. Performance-wise they're exactly the same, since SATA devices also have command queuing/reordering support (NCQ). SATA is found on the 'cheaper' drives, lacking the two above mentioned enhancements. SAS is the 'enterprise' standard, with some extra features: most of them come with dual ports (so they can be connected to two HBAs to increase availability) and they also have better diagnostics. It's important to clear up something: SATA vs SAS vs SSD is like saying APPLES vs ORANGES vs JAM - they are not of the same kind. So the choice is really about needed capacity / price / performance, but you should select enterprise-grade product, especially if you intend to use RAID. The second having, for example, more spare cells to replace used cells, more buffers, better trim management.Īlso, most of SSD use a SATA interface but now you will find SSD with SAS interface, making them the top choice regarding pure performance. SSD are also (like mechanical drives) divided into consumer-grade and enterprise-grade. SSD have good write performance and very good read performance, but are available in smaller size, or at equal capacity, are much more expensive. SAS protocol has enhanced features (for example queue re-ordering) that allow them to better manage I/O from multiple VMs and so they are much-more efficient (even with the same mechanical parts) than mechanical SATA for this usage. Mechanical SATA drives obviously have better prices but are in no way designed for such jobs, so for a serious business it's a no-go Given this, it's not very clear why there's even any market for 10k/15k SATA HDDs anymore - especially given that the capacities of these 10k/15k SAS HDDs are relatively similar and often even smaller than the capacities of the SSDs.It's a balance between price and performance. However, random IO is uncomparable - SSDs are faster by a factor of about 400x (4 hundred times). Of course, sequential speeds of 15k SAS HDDs (at about 250MiB/s on the outer physical layer (the beginning of the logical disc), and 100MiB/s on the inner layer (at the end of the logical disc)) are still relatively competitive with SATA SSDs (which usually do about 500MiB/s sequential throughput), because SSDs are reaching interface limits (6Gbps SATA is limited to 600MiB/s due to the 10/8 encoding) the difference is merely a factor of about 2 to 4x, whereas SAS HDDs would provide higher reliability. At random 4K read/write, that translates to 340MiB/s, which would appear to be faster than even the sequential speeds of latest-generation HDDs. (These IOPS parameters are limited by the speed of rotation, which stays constant through generations, and doesn't improve with each generation (unlike sequential throughput, which does improve with each generation).) Doing simple math around random 4K reads/writes, this translates to a performance metric of at most 800KiB/s - well under 1MiB/s.Ĭompare this with the specs for various SSDs that have been on the market for a number of years generally, the SATA 6Gbps (600MiB/s) ones appear to have reached interface limit, as they all appear to be spec'ed to about 85k IOPS for both reads and writes. At HDD: performance differences between 7.2k SATA and 15k SAS, we've determined that 7.2k RPM HDDs would have well under a 100 IOPS, whereas even 15k SAS would still only net you about 200 IOPS.
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