So just what is SVC – and what does Storage Virtualization REALLY do?


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With the move to the new blog software, there is probably a bunch of you that found yourself here, not knowing what this post was going to contain – as well as my regulars that either reap the benefits of SVC every day, or know the patter, but may not know all the benefits.

I liken SVC to a mobile phone. 10 years ago plus, a few of us had mobiles, some stayed away, but once you got one… how did you manage without. Thats how I’ve heard several of our customers explain SVC.

So that says its a must, but not what it can do for you.

In todays ‘smart planet’ and ‘dynamic infrastructure’ you need a storage environment that can stand up and hold its own against application and server mobility. Most of what the other major storage vendors can provide is inflexible. How often have I attended a briefing to be told “we are p**sed off being told, what you need is another box like the one you bought last year” – now there is one vendor in particular, that have tried to jazz up their mirror image trick box (think about that reference) that are really bad for it. They hate SVC. Why because we can show you don’t need that one trick pony, you can roll in a few of them, but replace a lot of them with much lower cost, modular, midrange boxes too. We have many customers, including some very large infrastructures that have made MAJOR savings.

That’s all very well, but how about managing lots of different boxes, and just how much can you manage as a single entity. Well think about your un-virtualizaed storage today. Every box is an island. Be it a DS8K, a few DS4K, a DMX, a Clariion, an AMS, or a USP. (I heard a rumour that HDS are qualifiying SVC as a downstream attachment to USP) – anyway… So you have a bunch of islands, even if you have a big box monolith that claims to virtualize, that big box is an island. With SVC you can seriously reduce the number of islands you need to manage – ideally one, but if you are out of scope then you probably have many 10’s or 100’s of boxes tody, at least being able to reduce that to 10’s is a step in the right direction.

Your company maybe acquiring others, consolidating disk, replacing disk, upgrading disk, or just trying to make better use of what you already have, with SVC it can all be made easier.

Today its typical that open systems run at way less than 50% capacity utilization – ignoring raid. With SVC we can help you to push that to much more like 75 or 80%. Now Martin G will be the first to say that he did that without SVC, but how painful a process was it. How easy was it to migrate between under and over utilized, not only from a capacity, but a performance stand point.

Getting back to where I started, what is SVC.

Virtualization, its a buzz word these days, what does it really mean. Well its an abstraction from physical to logical. I remember reading in “Inside NT 4.0” about the HAL – Hardware Abstraction Layer and thinking this was a cool idea. Little did I know that a few years later I would be part of the development team pioneering the same technique but in data storage.

SVC provides a way to abstract the physical location of data from the logical representation that an application on a server sees. So what? Well this means that the server and application only know about a logical entity. The physical entity can change, move, be replaced,  be replicated, be over-allocated, mirrored, migrated, snapshot… you name it… without any disruption to the server and application. Once you have an abstraction layer in the SAN you can do just about anything.

Witchcraft – no – reality. Understanding the fundamental concept that is virtualization of storage – and do note this is different to server virtualization – its not about making one look like many – its about the abstraction. This means you can move data without problems. So today you are paying a whole bunch of dollars for your backup, archive or stale data to live inside your Tier 0/1 controller, just because it was an easy sell to put some SATA in the spare drive slots. Really what you want to do is move that data to a midrange / entry disk controller that has some SATA. Maybe you need to mirror it between two SATA controllers because you don’t trust them, but two of them is a lot cheaper than the real estate populated by the big monolith with cheapy drives in it. You want to migrate down a tier, and not just in disk technology, but controller technology… BUT you may need access throughout. The abstraction that SVC provides means you can move the data without interrupting access, the “logical” still looks the same, but the “physical is very different.

So what does this all mean, well you acquire some legacy disk, you have some legacy disk, you buy some new Tier 0/1 disk and you want to efficiently tier (not monolithically tier) then you need a single system image that can span multiple physical boxes, but be managed in the same manner. You need IBM’s SAN Volume Controller (SVC) – not only does it help to reduce your costs, by reusing what you have. It can help to make better use of what you have, prolong the next purchase, save you capital expenditure, but also reduce you energy consumption – no need to expand as you have in the last few years – helping to reduce energy bills, reduce A/C requirements, replace those highly in-efficient boxes with the latest technology – all without interruption of service.

This all points to a ‘smarter planet’ – one which IBM is driving for, see how Forrester reads our Smarter Planet drumbeat, and of course you can read more and find links to related sites in the IBM Green Report

Comments copied from developerworks:

3 responses to “So just what is SVC – and what does Storage Virtualization REALLY do?”

  1. […] start by thinking about what I discussed last time and explained as an abstraction. Its what SVC does, separates the physical disks (RAID arrays) from […]


  2. SVC seems like a worthy idea, but how much more does it cost? Forty pounds? Eighty pounds? Regardless, I’m losing my chin hair thinking about how I coped before SVCs were introduced. Consider me a member of the TMBC on SVCs!


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