Wednesday, June 24, 2009

VMware I/O queues, “micro-bursting”, and multipathing

I colleague of mine came across this article and I had to share. It is a very technical read, but very relevant to all SAN environments. Anyone that is using VMWare should read this and understand the performance impact to your SAN.

“There was an interesting discussion/whiteboard around the topic of storage network design around FC/FCoE (though this applies to iSCSI as well). The Cisco folks made some really interesting analogies with VoIP and TP “micro-bursting” that I thought were awesome and I wanted to share.

It’s also the reason why there is so much discussion around LUN queues and queue management in vSphere. It’s not just EMC with PowerPath/VE, but I’ve heard 3Par start to talk about “adaptive queuing”, and last week Dell/EqualLogic announced their own addition to the Pluggable Storage Architecture. It’s all about the vStorage APIs, baby :-)

It’s apropos based on the recent discussion over queuing and comparisons of NFS and block-based storage options here.

Lastly, it’s also a topic of discussion based a recent post here on the topic of whether MPPs like PowerPath/VE are there to help “legacy” arrays and whether “virtualized” arrays get any benefit from more host-side sophistication. I’ve also heard the implication that NMP + Round Robin + ALUA are good enough in all cases – if you choose the right array :-)

Vaughn and I tend to agree a LOT – and we do, much more than we disagree. We both are super into VMware, which means there’s a lot of things we share. But there are times when we disagree – and this is one of them.

But this isn’t about EMC or Netapp, and isn’t personal, it’s core technical fundamentals – and apply to all storage vendors. If you want to understand and learn more – read on!

I will say this – with all arrays – EMC’s, HP’s, HDS’s IBM’s, and NetApp’s – all of them, the back-end design DOES matter, and you should look at it closely – and they are all wildly different architecturally. Each has their advantages and disadvantages – and usually what makes them an advantage in one circumstance is a disadvantage with another. This is why I’m personally of the opinion that it’s more about knowing how to leverage what you happen to have.”

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