Emergency service
- Article 24 of 26
- M-iD, October 2005
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Says BT's Voo: "Be pragmatic. Back up what you need to and don't back up everything. If possible, back up only the incremental changes. Not all data needs to be backed up constantly and if it doesn't change, you don't need to back it up." Given that in a full back-up, for every terabyte of data backed up, a further six or seven terabytes of storage may be needed (one terabyte per day with another terabyte for weekly backups), a full back-up can be very expensive.
This can only be done with the appropriate back-up or information management software. A content or document management system, for example, can help determine how often particular files need backing up. It can also provide administrators with the ability to analyse data usage, since it can keep an audit trail of how often files are amended.
The savings here can be large: as much as four-fifths of an organisation's data may be relatively static and so only requires infrequent back-ups. For example, old documents that are only occasionally accessed only need to be back-up once.
Content-addressed storage systems, such EMC's Centera, can be a boon in determining which files need to be backed up, since a file's name changes automatically whenever it is modified in such systems.
Technology needs
The organisation can then decide what technology it needs. Until recently, tape was the principle medium for back-ups on the grounds of cost. While it still remains the most affordable for smaller organisations, in the last few years price cuts have made disk-to-disk back-up systems more affordable for many medium-sized organisations.
Disk systems offer many advantages over tape, the biggest being speed - both for backing up and for restoring data. This has made 'continuous replication' a possibility: instead of having a scheduled back-up time for specific data, it is possible to duplicate data to a separate system whenever it changes. Continuous replication can work over a network and at a distance, making it applicable to failover, disaster recovery and data-loss back-up strategies.
It can also be of particular use for backing up email systems, something tape systems find hard to do. Systems from vendors such as Cryoserver use continuous replication to store all incoming and outgoing emails.
Paul Grossman, CEO of Cryoserver, says that organisations will often need to store certain emails for compliance reasons. "But since the average email user only uses half a gigabyte of email storage a year, you might as well back up everything."
One of Cryoserver's drawbacks is that it can affect the performance of email systems by as much as 20% or 30%, Grossman admits. However, this is as much a problem of continuous replication as Cryoserver's, since it will commonly affect directed attached storage in this way.
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