ORIGINALLY POSTED 15th November 2007

7,714 views on developerworks

There is a big difference to “in the switch” network based storage virtualization and “appliance” network based storage virtualization. Hu Yoshida and Dr. Kevin McIsaac, seems to have forgotten that in my comparison series of the three approaches to storage virtualization, both the appliance and array based approaches share most of the same benefits and, certainly with Hitachi’s USP models, nothing they can do we can’t with SVC – for MUCH less cost to the end users.

Hu is responding to an article quoting Dr. Kevin McIsaac recently posted on ComputerWorld. He sees it as, and I quote :

It was a brilliant article and one that I could not agree with more.

Now I guess he’s bound to think that as its trying to say – only in the array, with scare tactics of ‘more complex’ and ‘wastes money’ banded around in the article. I’d agree that something switch based, like Invista, that cannot perform true snapshot, FlashCopy, Replication or migration (in the way SVC and USP can) would limit what you can do. However, I really see the difference between USP and SVC as very small – in terms of the functions they are capable of. The biggest difference is vendor lock in With USP you are locked into HDS for the majority of their function and themselves claim that the external attach is really only for archive, backup or temporary access, not long term like SVC. Cost would be the next major factor.

My take is that this is a confusing article, making wild statements without any real evidence to back them up. I agree that you do basically negate the backend controller functions when you add something like SVC into the mix. But thats a bonus is it not? You now don’t have to pay for licenses on these controllers, you can write one set of scripts or tools that manipulate your backup and replication processes across the entire enterprise. You can online migrate data without having to make entire logical volume mirrors, you can tweak allocations to reduce hot spots…. You can buy cheaper storage – that doesn’t need anything more than enterprise level RAID technology. Thats why EMC and Hitachi don’t like SVC nor the idea of SVC – it does negate the functions in the controllers, I think it was Storagezilla that once said “SVC labotomises you arrays”. SVC has to, and in most cases does, provided the same functions as an enterprise controller. SVC also breaks from vendor lock-in, you don’t get locked into one vendor or supplier of storage. You can tender for who can supply your reliability and availability needs from a pure storage point of view, and who’s cheapest at that point in time. As long as its supported under the appliance, then you are much better off.

Anyway, I get wound up by people making misleading statements, and I’m sure most people can see through Hu’s ‘praise singing’ of this actually rather weak and obvious article. As for Thin Provisioning, its going to be something everyone thinks they want, and it will gain traction over the next few years – if you are interested in IBM’s roadmap, please speak to your IBM sales representative to discuss further – but there are caveats as BarryB has been discussing recently. It sounds great on paper, and as the surrounding ‘infrastructure of thin provisioning’ improves it will become more useable.