They see a shiny new storage chassis with 6G backplane. They fill it with “fast” drives, and build “raids” using integrated RAID platforms.
They insist it should be fast, showing calculations that suggest that it should sustain near theoretical max performance on IO.
Yet, the reality is that its 1/10th to 1/20th the theoretical max performance.
Whats going on?
In the past, I’ve railed against “IT clusters” … basically clusters designed, built, and operated by IT staff unfamiliar with how HPC systems worked. They share a number of traits, all partially or mostly anathema to high performance computing. I won’t re-hash that post, you can search for it.
Someone accused me of using IT as a pejorative … and this is incorrect. I am simply applying an appropriate label to a system.
Well, I think it is time to call out the same thing in storage. When you buy/build these sorts of storage units, you see low cost interconnect mechanisms which “sound” like they “should” work. Throw lots of SAS 10k or 15k RPM drives into these large SAS JBOD chassis. Only need one “RAID” card (and since its an IT designed cluster, its a pretty low end … HBA … with some RAID capabilities, but not a real hardware accelerated RAID).
And then your performance just sucks. C’mon now … 24 SAS drives should give me 2.4 GB/s, right? And with 8k random writes/reads I should get 300k IOPs, right?
Yeah, similar to a number of conversations recently.
No, I am not kidding.
Chances are, if you are doing this, or if your reseller/vendor is doing this, then you/they really haven’t matched your needs to the products capable of meeting those needs.
But we run into this. And we are sometimes engaged to help.
How do you explain to someone that their design, that they are so proud of, won’t work?
IT storage falls in this regard. Its great for bulk storage. Its fine for backups. Its ok for some low bandwidth low IOP service.
But its not so good for very intensive workloads. And thats an issue. Especially when they need the system to perform well under the intensive loads.
High performance ain’t easy. IT storage won’t get you there. Like IT clusters, they have designed in limitations. Like IT clusters, they have their strong supporters.
I should point out that we have nothing against IT, or IT folks, or IT processes. Its not a pejorative to point out a bad design. Or to label it as bad. But its problematic when you have to fight battles to solve a problem.
Just because something says 6G doesn’t mean its fast. Just because it says SAS doesn’t mean its fast.
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