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There are two usual reasons why tape drive are not be supplied with data at a sufficient rate. Firstly, rate at which data is read from hard disk of server is insufficient. This rate is dependent on sizes and locations of files on disk and is generally unpredictable, but can be determined by use of specialised software.
Secondly, if data is being transferred over a network of computers to a backup server, network may be incapable of supplying data at a sufficient rate. The maximum throughput of a network is predictable and easy to measure, based on previous network performance.
Consider a network using 10BaseT Ethernet. This transfer rate through this type of network cannot exceed 10MB/s, so it is immediately apparent that a tape drive requiring 20MB/s is inappropriate.
3. Reliability and duty cycle.
A simple way to gauge reliability of a tape drive is to find out Mean Time Between Failure (MTBF) as specified by manufacturer. You should note, however, that MTBF is usually specified at a certain duty cycle. For example, consider a Travan tape drive with a MTBF of 370,000 hours at 20% duty cycle. The drive will only have an average of 370,000 hours between failures if it is run less than 20% of time (about 4.8 hours per day), and running tape drive for any longer will significantly reduce reliability of drive.
There is no point purchasing highest-range tape drive if it's simply too expensive. Consider how much value-for-money tape drive will give you. Are you willing to pay more for extra performance? Or do you need to sacrifice some performance to save on costs?
If you choose wisely, you should end up with a tape drive that fulfils your organization's needs, without blowing budget.
Linus Chang is a backup expert and the lead developer of BackupAssist -- tape backup software that is simple and affordable, and perfect for small and medium businesses. Protect your Windows servers, including SQL Server and Exchange Server, to tape, REV drive, hard drive, NAS and more, at a fraction of the cost of other backup software. The product website is at http://www.backupassist.com