Up until about 6 months ago I was aware that the Hitachi range of enterprise storage had Copy On Write (CoW) snapshot functionality. But I had never seen, or heard of it being used anywhere….. that's right, anywhere! In fact any time I talked about it with my peers, we ending up authoritatively agreeing that it was not a technology suited to enterprise storage.
Add to that a training course I attended, where I wanted to play around with it (CoW) on a USP after class had finished. Only to find; myself, the course trainer and the lab manager fumbling through the GUI trying to find the button to create our first CoW pair – we later found out from the manual that pairs could only be done from the CLI!
So, in my admittedly small world, as little as may be 6 months ago, nobody used it or even knew how to.
Remember that Im talking about enterprise storage here. I'd used CoW technology a lot on midrange kit like the EVA, just never on a honkin enterprise array.
Fast forward to now, where I've seen two back to back USP installations using CoW and consider myself a world authority on the technology 😉
So what has changed? Was I wrong 6 months ago, is CoW snapshot technology suited for enterprise storage?
If I take a look at the installations Ive recently worked on, they both still use full block copies, using ShadowIamge, to back-up their critical applications such as Oracle and Exchange. One is using CoW for backing up less critical systems, and the other is using it as a space efficient method for keeping multiple daily file server backups (with a 1 hour granularity).
So with this in mind it kind of looks less like CoW is creeping into the enterprise space, and more like enterprise storage is creeping down into the space of midrange storage.
Interestingly, both CoW implementations have been on small USPs. One is a single cabinet (DKC only) and the other is a 2 cabinet installation and both have external storage hung off the back. And in my experience, this trend of buying smaller USPs, instead of traditional midrange kit, is becoming more and more common, and I suppose it makes a lot of sense. For example, it provides all of the following –
1. Fits today needs, with enterprise class features for a moderate price
2. Provides wide range of functionality and therefore flexibility (midrange and enterprise features)
3. Allows for large internal expansion
4. Ability to prolong the life of older storage by hanging it off the back, if you should so desire
5. Allows for future expansion via external storage
Compare this to purchasing a midrange box. Although a midrange box would normally still be cheaper, it would provide may be only one, in fact only half of one of the above features (1)
Add to this the diskless NSC from Hitachi. Providing the functionality of enterprise AND midrange (CoW 😉 ) in the NSC controller and allowing you to hang any Tom, Dick or Harry's disks off the back.
So where does midrange storage fit in? 3PAR?
NB. I see that Anil is doing the 3PAR thing this month <link here>