Evaluation criteria for backup devices
1) Reliability (MTBF) mean time between failures. Backup drive should be reliable with minimal failures. In general, moving parts in devices make them prone to failures. Do independent research.
2) Duty cycle. %age of hours per total hours in a day that the drive can remain operational. A drive supporting 12 hours continuous operation has a duty cycle of 50%.
3) Native data transfer speed. Important to ignore compression rates as it is dependent on the data.
4) Flexibility to use the media is how the media can be emulated to server as another media type and how media can be best used. Tapes should be streamed to the maximum throughput, otherwise they spend half their time repositioning the tape head. Hard disk can act as tapes (virtual tape library)
5) Capacity of media is now less important with the advent of autoloaders. But it should be considered particularly where restoration is preferred over a single media/volume.
6) Compression can be hardware or software based. Hardware compression is done the chip on the backup drive whereas software compression is host CPU intensive.
7) Equally important to data transfer speed is the disk access time. It is the time taken to locate the needed information and place the drive head over it. Tapes being sequential media are worst performers in this regard.
8) Lifetime is a measure of how long the media can be used. Tapes, which are constantly used in non-streaming media do not last their stated maximum reads/writes and will need to be changed much earlier.
9) Cost is an important criteria. In addition to media cost, cost of drives, backup preparation/administration required for particular type of backup needs to be considered. For example, tape based backup may require operator onsite assistance for tape mounting, retrieval and storage.
2) Duty cycle. %age of hours per total hours in a day that the drive can remain operational. A drive supporting 12 hours continuous operation has a duty cycle of 50%.
3) Native data transfer speed. Important to ignore compression rates as it is dependent on the data.
4) Flexibility to use the media is how the media can be emulated to server as another media type and how media can be best used. Tapes should be streamed to the maximum throughput, otherwise they spend half their time repositioning the tape head. Hard disk can act as tapes (virtual tape library)
5) Capacity of media is now less important with the advent of autoloaders. But it should be considered particularly where restoration is preferred over a single media/volume.
6) Compression can be hardware or software based. Hardware compression is done the chip on the backup drive whereas software compression is host CPU intensive.
7) Equally important to data transfer speed is the disk access time. It is the time taken to locate the needed information and place the drive head over it. Tapes being sequential media are worst performers in this regard.
8) Lifetime is a measure of how long the media can be used. Tapes, which are constantly used in non-streaming media do not last their stated maximum reads/writes and will need to be changed much earlier.
9) Cost is an important criteria. In addition to media cost, cost of drives, backup preparation/administration required for particular type of backup needs to be considered. For example, tape based backup may require operator onsite assistance for tape mounting, retrieval and storage.
posted by Usman Wahid at
10:44 AM
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