An explanation of IOPS and latency

<I understand this extremely long post is redundant for seasoned storage performance pros – however, these subjects come up so frequently, that I felt compelled to write something. Plus, even the seasoned pros don’t seem to get it sometimes… 🙂 >

IOPS: Possibly the most common measure of storage system performance.

IOPS means Input/Output (operations) Per Second. Seems straightforward. A measure of work vs time (not the same as MB/s, which is actually easier to understand – simply, MegaBytes per Second).

How many of you have seen storage vendors extolling the virtues of their storage by using large IOPS numbers to illustrate a performance advantage?

How many of you decide on storage purchases and base your decisions on those numbers?

However: how many times has a vendor actually specified what they mean when they utter “IOPS”? 🙂

For the impatient, I’ll say this: IOPS numbers by themselves are meaningless and should be treated as such. Without additional metrics such as latency, read vs write % and I/O size (to name a few), an IOPS number is useless.

And now, let’s elaborate… (and, as a refresher regarding the perils of ignoring such things when it comes to sizing, you can always go back here).

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Questions to ask EMC regarding their new VNX systems…

It’s that time of the year again. The usual websites are busy with news of the upcoming EMC midrange refresh called VNX. And records being broken.

(NEWSFLASH: Watching the webcast now, the record they kept saying they would break ended up being some guy jumping over a bunch of EMC arrays with a motorcycle – and here I was hoping to see some kind of performance record…)

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FUD tales from the blogosphere: when vendors attack (and a wee bit on expanding and balancing RAID groups)

Haven’t blogged in a while, way too busy. Against my better judgment, I thought I’d respond to some comments I’ve seen on the blogosphere, adding one of my trademark extremely long titles. Part response, part tutorial. People with no time to read it all: Skip to the end and see if you know the answer to the question or if you have ideas on how to do such a thing.

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