Storage Virtualisation

FAQ
One of the eternal problems of systems management is that there's so much of it. As system components get more complex and capable, deploying and controlling them gets no simpler. Storage is particularly prone to this: you can never fit and forget a storage device: it will get full, need backing up and kept in a reliable condition. This problem gets more complicated with every different piece of storage attached to your system, and live data is particularly unforgiving. Storage virtualisation aims to fix this. It works by gathering together disparate storage devices and presenting them to a server as a single logical entity: one point of management, plus greater ease of attaching and detaching extra storage. With decent caching and bandwidth management, usually courtesy of a storage-area network (SAN) running on Fibre Channel, performance and reliability are also enhanced -- or so claim the vendors. This is nothing new -- RAID systems are simple virtual storage systems -- but while the idea has many advantages, the costs and disadvantages have led to many companies adopting a wait-and-see policy. There are three main virtual storage architectures -- in-band, out-of-band, and host-based. In-band has the virtual storage management box sitting between the applications and the storage devices -- it processes all transactions, acting much like a network router. Out-of-band doesn't mediate every transaction, but sends information about where the transactions are to go to the applications: the analogy here is a DNS server. Host-based systems have virtualisation software running on each storage host. Each architecture has trade-offs. In-band storage moves everything through one point, and is thus in danger of becoming a bottle-neck -- there goes the scalability. It also increases latency. Out-of-band systems don't impede the flow of data between application and disk, but you can't mix and match options from different companies. Host-based systems are also free from bottlenecks, but as each storage server needs additional software there is considerable extra management required. This negates the main benefits of storage virtualisation, simplified management -- in the ideal case, one management console covering all storage across the enterprise. In-band is proving the most popular, usually with the virtualisation managed by an Intel-based server running Windows or Linux. This must be powerful -- there's no point in having such a system if it's serving another server that's got a higher IO throughput -- and vendors and analysts alike warn that reliability has to be explicitly addressed. And while out-of-band virtualisation avoids this problem it does require software to be installed and managed on every server on the system. Such approaches tend to be proprietary, making them hard to integrate across multiple vendors' equipment and difficult to manage. This lack of standardisation has long hindered storage virtualisation That's changing. Following a number of initiatives, the Storage Networking Industry Association adopted a standard called Bluefin -- now officially known as the Storage Management Interface Specification, SMIS, as well as sometimes just SMI or SMI-S. It's an attempt to make storage devices and storage area network management consoles work together. SMIS takes some existing standards such as CIM -- the Common Information Model, which describes the management requirements and capabilities of systems -- and the Web-Based Enterprise Management, WBEM, and specifies how they should be used. This includes ways to discover CIM managers on networks, how to take control of subsystems co-operatively with other management systems, and so on. By using the ubiquitous mixture of XML and SOAP, SMIS aims to make storage management as open a field as other areas of IT have become through SNMP and its progeny: to that end, EMC, Brocade, IBM, Hitachi, Brocade, Veritas, Hewlett Packard, Sun, Dell, Intel and StorageTek among others have joined in. Microsoft is an associate member of SNIA, but at the time of writing was unable to say whether Server 2003 and associated storage aspects -- Windows Powered NAS (WPN), Virtual Disk Service (VDS) and Volume Shadow Copy Service (VSS) would be SMIS compliant. We suspect it will be, as Microsoft has formed strategic alliances with people such as HP, but the company's history on open standards is mixed. While storage virtualisation has improved over the past year, there are still many questions to ask of any product. Will the system merge with your existing management tools? How scaleable is it? How does it affect backup and restore strategies -- how long does it take to take an image and rebuild it? Is it fault-tolerant? Can you add storage from other manufacturers? Has anyone else installed such a system to manage comparable amounts of data, and what's their telephone number? Only if you get good answers in all of the above areas -- any of which can ruin your weekend -- should you start to get onto costs and benefits. Confidence in storage virtualisation will only come with a history of successful deployment in heterogeneous environments and plenty of stories of tangible gains. The technology is still more promise than delivery, but with continual and substantial development taking place it has every chance of being ready for action when the current stringencies fade out.
For a weekly round-up of the enterprise IT news, sign up for the
Enterpise newsletter. Find out what's where in the new Tech Update with our
Guided Tour. Tell us what you think in the
Enterprise Mailroom.

Post your comment

In order to post a comment you need to be registered and logged in.

You can also log in with Facebook. Log in or create your ZDNet UK account below

  • Login

Will not be displayed with your comment

By signing up for this service, you indicate that you agree to our Terms and Conditions and have read and understood our Privacy Policy. Questions about membership? Find the answers in the Community FAQ

Get ZDNet UK's daily newsletter

Enter your email address to sign up

ZDNet UK Live

Moley

@ewallace. Not so clear. Anyone can obtain the text, for example from here http://www.ustr.gov/webfm_send/2379. I support ACTA so long as it and...

6 minutes ago by Moley on ACTA: Facts, misconceptions and questions
45283

I think WinRT is fantastic. I just wish it was an option for people that didn't want to go through Microsoft's App Store with its attendant...

3 hours ago by 45283 on Why Windows 8 needs architectural hygiene for WOA
Burn-IT

Nine people? £30m? Who's back pocket is that lot going in? And IF they say it is for new buildings, what about all the ones the government has...

4 hours ago by Burn-IT on Police set to launch three £30m e-crime hubs
ewallace

Just to be clear, nobody knows what is in the text of ACTA, here is a photograph of the text of ACTA http://twitpic.com/8h9iju as submitted to the...

4 hours ago by ewallace on ACTA: Facts, misconceptions and questions
fgvrg56

Unfortunately main issue is that ASUS is refusing to accept that they make some mistake on this version of asus Transformer prime. 1 - GPS sensor...

6 hours ago by fgvrg56 on Asus Eee Pad Transformer Prime Wi-Fi & GPS problems?
Ben Woods

@Marcus A fair question. Just talked with Archos which said it was working on an announcement for next week....

7 hours ago by Ben Woods on Archos confirms G9 Ice Cream Sandwich update schedule
Marcus Karlsson

Any update on this, considering the claimed "first week of February"?

8 hours ago by Marcus Karlsson via Facebook on Archos confirms G9 Ice Cream Sandwich update schedule
apexwm

Bill Goodrich : Just as al_langevin pointed out, with Windows Server 2008 there is no Services for Macintosh anymore. It's gone, not available....

16 hours ago by apexwm on Windows Server 2008 drops the ball for Mac compatibility
txtrainguy

Replying to an old topic that I'm currently facing with my CEO (who is on a Mac). Our servers are primarily Windows Servers, office is about...

23 hours ago by txtrainguy on Windows Server 2008 drops the ball for Mac compatibility
k0tcs3

Sure, that makes perfect sense. Pay wrong-doers money and thank them for breaching your security and pointing out your flaws, that would surely...

23 hours ago by k0tcs3 on US indicts Romanian over NASA climate change hack
Random_Error

I think he's referring specifically to Android apps, as Apple do regulate their App Store, but Google seem to let any old crap onto the Android store!

23 hours ago by Random_Error on RIM: BlackBerry will keep 'garbage' apps out of store
Paul Fezziwig

Keep the crap apps out?! How will they compete with Android and Apple's claim to fame of having so many life changing apps? I wonder if the media...

1 day ago by Paul Fezziwig via Facebook on RIM: BlackBerry will keep 'garbage' apps out of store
Aigars Mahinovs

It has been shown time after time that if there is an author store that sells the songs at even 1$ per song and gives you a high-quality digital...

1 day ago by Aigars Mahinovs via Facebook on Copyright isn't working, says European Commission
awbMaven

""As a result of Butyka's alleged conduct, researchers were unable to use the computers for more than two months while NASA removed the malicious...

1 day ago by awbMaven on US indicts Romanian over NASA climate change hack
subhorup

It simultaneously worries me and uplifts me that a self-proclaimed group of internet activists name themselves after Indian mythical figures....

2 days ago by subhorup on Anonymous activists release PCAnywhere source code
naviathan

It's actually far easier to work anonymously on the internet than you think. With tools like Tor bouncing your traffic around the world before...

2 days ago by naviathan on Anonymous activists release PCAnywhere source code
Agnostic_OS

1000272134 and bluedalmatian with you both there but then I'm still in 10.04 land (and happy with it)

2 days ago by Agnostic_OS on Ten factors that make Ubuntu 11.10 a hit
apexwm

Interesting article and definitely see your points on the products mentioned. One of the top products for our Help Desk (approximately 20% of all...

2 days ago by apexwm on Ten flawed products that derail productivity
Paul Hutchinson

Absolutely - this should obviously not be handled my isp - but handled by their hosting operator. What's been suggested here is that my isp police...

2 days ago by Paul Hutchinson via Facebook on MPs urge ISPs to take down terrorist material
Techs UK

Looks like a great phone. I don't notice any deficiencies in WP7. used IOS before, that's pretty good. I don't spend much time in Apps, all i need...

2 days ago by Techs UK on Nokia pins US 're-entry' hopes on Lumia 900