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Disk vs Tape

Disk based storage technologies are not exactly new, but capabilities such as disk snapshots, journaling and off-site mirroring have made it a viable solution for use in backup and business continuity strategies. By Dr Carl Windos, chief technology consultant for TeleCity.


Date: 1 Oct 2005

In recent months, there have been several articles proclaiming the death of the tape backup industry. Small percentage revenue growth among some of the leading vendors is cited as a signal that tape is coming to the end of its useful life , whilst disk vendors are thriving and experiencing double digit growth . Whilst not exactly great news for the industry, neither is it that surprising; tape backup is a mature technology with an already high market penetration, and generating exponential new business growth is always more challenging in a mature market. Add to this the fact that a large proportion of the increased revenues reported by disk storage vendors will likely be purely for consolidated live data storage (as opposed to near or off-line data backup and archival - a market in which tape backup does not compete) and it becomes clear that these comparisons are not particularly useful to someone looking for an appropriate backup solution.

There are several commonly quoted drivers for wanting to migrate away from tape-based backup solutions . The most common of these are to:

? improve backup-and-recovery processes
? improve business continuity and disaster recovery processes
? reduce operational expenses associated with tape libraries
? reduce capital expenses associated with tape libraries

However, with a correctly-configured and well-managed tape-based platform, these issues should not occur. In fact, it is likely that migrating away to a disk solution will likely increase overall costs and not necessarily improve business continuity processes. If the processes were not working efficiently with a tape-based solution, there is no reason to think a change of technology will improve matters. More often that not, a review and overhaul of processes and procedures will resolve most ?issues? with existing tape based solutions. Indeed, without such a review, a change of technology could lead to a zero improvement the backup function.

Of course disk-based solutions do offer some unique benefits. Disk backup technologies such as snapshots and transaction journaling provide a frequency and resolution of rollback capability which, with current technology, tape could not achieve. This is an ideal backup method to utilise for rapidly changing, mission critical data. Near-line backup methods utilising this type of disk technology are being hailed as the future in data backup (but most usually by the storage vendors themselves) and whilst benefits exist, organisations considering a migration of strategy should bear some other things in mind.

Organisations considering an in-house, near-line storage option need to ensure that it is totally separate to the primary disk storage subsystem. If this is not the case, they are putting their business at risk of data loss. As already mentioned, business continuity is a common driver in backup requirements and having all data in a single location does not provide adequate protection. Storage arrays are ultimately a form of RAID disk array (albeit with some additional, intelligent technology controlling it). If an organisation was to experience a failure in an array containing both live and backup data, it could end up without any data to restore. The risk of this can be mitigated by mirroring the array, but unless the array has been mirrored to a secondary location, there is still a significant risk to the availability of the data. And while a mirrored system may be a valid technical solution for the requirement, it will not always be suitable for cost reasons as it doubles the hardware required and has the additional DR site and networking requirement. Tape backup solutions do not have this limitation as the data can be vaulted off-site to be recovered should the worst happen.

The data retention period and rate of change of data should always be considered as this will contribute significantly to the growth of the storage requirement, no doubt to the delight of your chosen vendor?s account manager. It is the long term storage where disk based backup is unable to compete at this time. For example, what would happen if an organisation were to attempt to restore a corrupted data set, only to find that it had been corrupt for some time and all of the disk snapshots were also corrupt? On tape, there would be the option of rolling back to copies taken days, weeks or even years ago. Proponents of disk backup technology would argue that this issue could be overcome by the addition of extra disks to the storage array, but at $15-20 per MB compared with $0.001 per MB for tape media the cost of incrementing disk storage capacity could quickly become higher than the value of the data it is protecting.

With the introduction of new regulations such as the Freedom of Information act and Sarbanes-Oxley, the requirement for long term storage is set to increase significantly for the foreseeable future. For this reason, we can reasonably predict that the future for low cost, long term tape backup is a good one.

TeleCity, in partnership with storage experts MSI, has developed a solution that understands the functionality of each media and delivers a solution suited to the individual customer requirements; combining the required backup methods (near-line storage, e-mail archival, tape backup, off-site vaulting) and business continuity collocation and high speed networking, if and when required. Contrary to perception, in the majority of cases, our fully managed tape backup system meets all customer requirements and is the lowest cost solution.

With a recent survey stating 71% of respondents were planning to purchase tape storage and 64% planning to purchase disk based solution this year , it appears that the consumers have come to the same conclusion; that the technologies can happily coexist. With 3.5% of the respondents in the same survey looking to outsource their backup to a third party storage provider, TeleCity is well placed to deliver a cost effective solution that is not driven by the technology or physical location but by the customer?s specific requirement.

Dr Carl Windsor
Chief Technology Consultant

For further details, please contact:
Sally Bratton, Bratton PR
t: +44 (0)1895 477770; e: [email protected]

James Tyler: +44 20 7519 4858
Email : [email protected]


Tags: Data Centres

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