From the “EMC VNX Unified Best Practices for Performance – Applied Best Practices Guide” August 2012 which is the latest release currently available.
On page 12:
<SNIP>
Rules of thumb for drive performance:
These are a conservative starting point for sizing, not the absolute maximums.
IOPS assumes small block random with good response time.
Drives are capable of a sustained IOPS workload based on drive type, as follows:
IOPS
NL-SAS 90
SAS 10K 140
SAS 15K 180
Flash 3500
For IOPS with spinning drives (SAS and NL-SAS), VNX models scale linearly with additional drives, up to the maximum drive count per model.
Bandwidth assumes large-block sequential with multiple streams.
Spinning drives provide about 30 MB/s of bandwidth capability; Flash drives provide about 100 MB/s.
</SNIP>
There is no difference in IOPs and Bandwidth between 3.5 and 2.5 inch drives. Both will deliver the same.
If you are coming from a CX with FC and SATA drives, you will see a huge performance gain, not only because of the faster processors in the SPs, but also by moving to a SAS backend bus.
The other thing you might want to keep in mind, and it is very minor is the Access Time difference between a 10K and a 15K drive.
From: H8514 – VNX Series SS.pdf (EMC VNX Series Unified Storage Systems – Specification sheet)
For comparison only, please download the document for all the details.
600 GB 15K drive
Access Read: 3.4 msec
Access Write: 3.9 msec
Rotation Latency: 2.0 msec
600 GB 10K drive
Access Read: 3.7 msec
Access Write: 4.2 msec
Rotation Latency: 3.0 msec
You see that the differences are very minimal, but not knowing your use case, this might or might not be important to you.
There are lot of discussions that the 10K drive can deliver almost the same amount of IOPS than a 15K drive for a lot cheaper price. Some places like this document say 140 IOPS for a 10K drive, other docs says 150 IOPS for a 10K drive. So that makes the difference 150 to 180 IOPS, that makes it worth the discussion, can you get away with 10K drives instead of 15K drives.
What a lot of people are also talking about is that 15K drives will disappear in the near(2-5 years) future and there will only be 10K drives around (besides Flash and NL-SAS of course). Those discussions have been around for a while but do I believe that they will be phased out with Flash becoming cheaper and cheaper.
Hope this helps.
Fred van Donk
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