Dropping a load off the Lan

Feature

Dropping a load off the Lan

The huge growth in online data storage that has come with the Internet age is changing the nature of backup operations.

A revolution in backup procedures is taking place, according to Gartner Dataquest chief analyst Carolyn DiCenzo. "Sans, intelligent storage appliances and new data replication techniques will transform the way storage backup and recovery is accomplished over the next three years," she said.

These new technologies are emerging in response to a real and pressing need. As Peter Coleman, FCIA Europe president, put it: "Five years ago you might have 100 Mb to back up, which you could do in three hours; that has become 3-4Gb, but you've still only got three hours."

You can't put a quart into a pint pot, and in many cases you haven't even got the option of trying. E-commerce has meant a steady move to 24x7 operations even for relatively small organisations.

The result is that the traditional client-server method of backing up the data created on the network each day during the night is increasingly no longer possible: there's too much of it, and the backup process itself degrades the performance of the increasing number of other overnight processing tasks.

The major development designed to overcome these problems is the so-called Lan-free backup. The name is a bit of a misnomer, as Mike Quinn, Quantum ATL European product marketing manager, explained: "Lan-free backup is a really nice phrase, but at the end of the day you need a Lan, even if it's a private one. A San is in effect a Lan just for data. You're freeing up the network you have, but you're putting in another one."

The key enabler for Lan-free backup is Fibre Channel connectivity. This was introduced in the early 1990s for improving transfer to and from disk, both internally within subsystems and externally to servers. The use of fibre optic cabling had two benefits over the prevalent copper SCSI cabling; it substantially increased the maximum distance between peripheral and host (from a few metres to several kilometres) and it significantly improved performance.

Towards the end of the '90s this capability became available on tape drives and libraries as well. It is still not common in the mid range and below - Overland Data estimates that only 8 per cent of systems are currently sold with Fibre Channel connectivity - but it is becoming increasingly so. Attaching a tape drive via a Fibre Channel link to a server gives you the benefits of performance and distance, and also allows you to take at least some of the backup traffic off the Lan.

But most users are going the extra step and installing a storage area network (San). At its simplest, this means putting in a switch between the online storage, the tape drive or library and the application servers that need to use them.

Switches cost increasingly less, and offer a number of benefits. It is easier to connect and disconnect both storage devices and servers without disrupting existing work, and it minimises recabling when new devices are added.

Most users find it relatively easy to see a return on investment when installing a San for backup, especially when it is done in conjunction with consolidating storage. A recent MacArthur Stroud survey showed that just under one fifth of companies surveyed had installed a San: of these, 86 per cent (more than six out of seven) were using it for backup.

Users who wish to retain tape libraries with SCSI interfaces can still take advantage of the benefits of San by installing a SCSI-to-Fibre Channel bridge. This type of product is offered by companies such as Chaparral Network Storage. So using a San can free up the bandwidth of the existing Lan to improve the performance of client-server applications. It also offers better performance than traditional SCSI based storage, and permits siting of storage devices at greater distances from their hosts. But "the real benefit", said Coleman, "is Lan-free restore". He argues that when one of several servers on a Lan goes down, restoring it affects the performance the users of the other servers get. With Lan-free there is no such effect.

These benefits have stimulated the take-up of Lan-free software over the past couple of years. Veritas reports it is selling a lot of its product, Shared Storage Option (SSO), which is an add-on to either NetBackup or Backup Exec. Overland Data's European marketing manager Howard Rippiner estimates that around one third of shops running multiple servers now use Lan-free.

With a Lan-free architecture, however, the server is still involved in running the software from the likes of Computer Associates, Legato and Veritas to make the backups occur. This is not so much a problem if the server being used is dedicated to storage tasks, as in the case of a network-attached storage (Nas) filer, but can be very disruptive on servers used for transaction processing or for other 24x7 client applications.

Two further developments are emerging to address this problem. The first is the use of snapshots, a technique originally introduced by StorageTek to the mainframe world in the early 1990s. Here a point-in-time copy of a database is made by creating pointers to the whole content of the database at the given moment. Each time any part of the database is updated, the new datum is written in an unused part of the disk leaving the original one unchanged.

As a result, it is possible to access the database both as it currently stands and as it stood at some specified point in the past. This allows backup systems to back up a "frozen" copy without disrupting live processing. You can make a snapshot in a couple of seconds and back it up at your leisure.

The second new development is server-free backup, an application that has developed since the arrival of the San and which requires you to have a San. The principle here is that you have a piece of software incorporating a data mover agent which sits in a device within the San that is not a server - a bridge, a router, a hub, or even a tape drive. The backup software sitting in the server issues a backup request to this device, which then takes over and manages the backup between disk and tape, reporting back to the server when it is finished. In the meantime, the server is free to carry on performing all its other tasks. Restore works in exactly the same way.

Apart from freeing the server, this technique also improves backup performance, as it is not being inhibited by any other process. Some estimates suggest backups take place 50 per cent faster as a result.

Veritas was one of the first companies to introduce a serverless backup software product with its ServerFree Backup Option, launched a year ago under the code name Vertex.

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This was first published in December 2001

 

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