Special Report

Unified storage simplifies things for admins managing NAS and SAN

For most storage administrators, using both SAN and NAS systems to access files means that there are two lots of administrative tools: one to manage and provision the SAN and another to look after the NAS. And in most cases, using both SAN and NAS means that there are two pools of storage.

One method that storage administrators can bridge that divide is unified storage: a single system capable of delivering block-based storage from a SAN and file-based NAS via CIFS and/or NFS.

SAN and NAS: Not so different beneath the surface

SAN and NAS used to be regarded almost as fulfilling opposite roles in storage environments. A SAN delivers blocks of data to server file system requests while NAS, with its on-board file system, serves complete files to users.

Both SAN and NAS systems serve specific purposes. Some applications, such as databases, work best from a SAN, dipping in and out of the component blocks of a single large file. Others applications need to access entire files, such as office productivity documents or images, from a NAS subsystem that is easy to configure, share and back up.

Beneath the surface, SAN and NAS are not so different. Indeed, all storage is block-based when you get down to it, and large NAS systems have something like a SAN inside the box. It's also possible to attach a NAS head to an existing SAN, give it some LUNs, and have it access data at file level.

 

What has really shifted unified storage up a gear is iSCSI. Most unified storage systems include Fibre Channel SAN access, but for many companies, the ability to use the same network infrastructure for iSCSI SAN and NAS is a big plus.

That type of consolidation was what attracted Sutton & East Surrey Water to NetApp's FAS filers, says Michael Cock, operations manager. The utility wanted block-based iSCSI storage for its database and Microsoft Exchange applications, CIFS file shares for its Windows users and NFS file shares for applications running under Solaris.

The ability to manage both NAS and SAN from one point was what persuaded the water company to choose NetApp over its other short-listed supplier, Dell/EMC.

"If the pool wasn't shared, we'd be using a multiplicity of tools," Cock says. "It's consolidation squared -- we consolidated all the file shares, and we consolidated file and block. It all comes off the same disk area, it's just that you can set up an area as an iSCSI share.

In the water utility's unified storage environment, rather than put HBAs in every server, Cock chose to go with a group of disks serving NAS, and for SAN disks serving iSCSI. Each server has two NICs, one connecting to the filer and the other to the LAN.

For Cock, unified storage is easy to admninister. He says, "It takes approximately half an hour to set up the LUNs to fully provision storage for a new SQL Server. It is just three or four clicks. When we had Veritas Volume Manager on Unix, every change required downtime and the attention of a trained storage administrator."

The utility's one concern was whether unified storage could meet the performance requirements of its block-based applications. So the company took care to run the migration in phases -- and it also took out some insurance with its supplier as well.

"We approached it application by application and server by server, spreading the project over a reasonable time," Cock says. "We had very few worries about Exchange and SQL Server performance because lots of people already use those on NetApp.

The company's largest database is its CRM and billing system. "That's not a tier 1 application," Cock says, "so we had less evidence of how it would perform. So we made its performance part of a sale-or-return agreement."

Reduced storage management effort
Gavin Wood, the systems administrator at telco HTK, says that using a single device -- in his case, an EMC Celerra NS40 IP storage platform -- to provide NAS and iSCSI block access has reduced the amount of time and effort he spends on storage management.

"It's all managed through the EMC administration module -- partition usage, everything," says Wood. "I see the NAS partitions exactly the same way as the iSCSI partitions. It saves us monitoring separate devices and there's only one device to support, though it looks like two on the network."

Like many other iSCSI users, HTK chose to separate SAN and NAS traffic. Each server has two network connections – one fully switched Gigabit Ethernet for iSCSI, and a second for NAS and the LAN.

One problem with unified storage is that although it looks like two data movers on the network, there is only one disk infrastructure. "You've got to be careful where you're putting data," warns Wood. "For example, you can't back up your iSCSI data onto the NAS!"

 I see the NAS partitions exactly the same way as the iSCSI partitions. It saves us monitoring separate devices.
Gavin Wood
systems administratorHTK

While the Celerra performs well when serving high-speed protected NAS to business-critical applications -- HTK uses it to store voicemail -- it can be overkill for general-purpose use. "We have begun looking at cheaper NAS," Wood says. "There are times when you just need shared storage for documents."

Chance to consolidate NAS
For some storage managers, unified storage arrives almost by accident. They get the storage gear to solve one set of problems, and then find it can do other things too.

At Birkbeck College's School of Crystallography, the original plan was to buy an iSCSI SAN and use it to centralise and consolidate the school's storage, then add replication and mirroring for disaster recovery. However, when one of its suppliers suggested a unified storage system, the school's head of IT, Richard Westlake, realised he had the opportunity to consolidate NAS as well.

The school now has a pair of Reldata 9240 Unified Storage Gateways, which deliver iSCSI SAN, NAS and WAN replication functions from a single virtualized storage platform. Birkbeck also uses storage arrays from Dot Hill Systems for both NFS and iSCSI. It plans to use them for CIFS file sharing too when its existing Samba file servers give up the ghost.

Westlake says that as well as enabling him to impose some discipline on a diverse set of projects, each with its own budget for buying storage, the unified approach has allowed him to stretch his resources twice as far.

"We are very limited in budget, for both initial capital and recurrent expenditure," he says. "We use both block and file – most clients use NFS, but some applications we have, such as our Unix email system, do not run nicely on that.

The school bought its storage as a complete kit from one provider to avoid vendor finger-pointing. Having two storage controllers provides fault-tolerance plus some load balancing. "In theory we could buy more iSCSI storage and attach it to the Reldata for virtualization," says Westlake. "Not having a closed monolithic system was important to us."

The main issue that Westlake has with unified storage is getting enough data through the box. Each Reldata 9240 has dual Fibre Channel ports and four Gigabit Ethernet ports, but while newer models have 10 Gigabit Ethernet, Birkbeck College can't yet afford a 10 Gigabit core switch. According to Westlake, "We might consider 4-gig Fibre Channel instead for demanding applications, just to get the bandwidth out of the box."

Stumbling block may be politics
Freeform Dynamics analyst Tony Lock warns that the biggest obstacle for many organisations adopting unified storage is politics. The SAN is usually managed by the storage group, while NAS is often the responsibility of the network admin or an application group.

"The most common thing is people have physical storage devices and they want to turn them into a pool," Lock says. "Many organisations are not able to use that pool for block and file though, because they are siloed."

However, in today's economic climate, unified storage could be the weapon that IT departments need to break down those silos, suggests Clive Longbottom, service director at analyst group Quocirca. He says IT needs to make the business aware of the cost savings and greater efficiencies possible with unified storage. One way to do that is by carrying out a review of the storage assets.

"Storage tends to grow organically," says Longbottom. "And while anyone in the business might realise it's unsustainable to have all those different blocks of storage, they're not be aware it is happening."

"IT has to go in and talk the business's language," he says. "In a downturn market, IT has to be an investment -- and unified storage is a damn good investment for many."

 

This was first published in December 2008

 

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