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#61
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In comp.sys.ibm.pc.hardware.storage David Magda wrote:
Arno Wagner writes: Good idea. This is really just "persistent buffering", a quite old technology, e.g. implemented in many tape-library storage systems. But please use at least 3 independent sets of tapes with this too and verify the readability of your tapes at regular intervals. Any reason why three should be used? 2 is simple: While you do a backup, you destroy one. So if you discover a problem with the original while making a backup, and you have only one medium, you are entirely without backup _and_ have a damaged original. My personal reasons for 3: - If you only have 2 and then one of the media dies, you run into the problem above. - It adds some redundandency. 2 is clearly the minimum. So 3 adds a safety margin, i.e. when one medium dies you can still an additional backup. - If you backup device/software breaks and kills the medium (for whatever reason, can also be a virus, etc.), you are likely to assume medium failure first and try with the second medium. If that breaks also, you still have one good backup. - Other good reasons I am not aware of. It seems to be common wisdom among sysadmins... Actually many admins think that 3 backups are too little, because you get too little history. Still, better any backup than none, but don't feel to safe even with backup. I admit that you can work with 2 medium sets, if you get a replacement _immediately_ in case one of the media fails. Arno -- For email address: lastname AT tik DOT ee DOT ethz DOT ch GnuPG: ID:1E25338F FP:0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F "The more corrupt the state, the more numerous the laws" - Tacitus |
#62
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Arno Wagner wrote: I admit that you can work with 2 medium sets, if you get a replacement _immediately_ in case one of the media fails. Since 2 Days i use a DLT to save Backup Images to Tapes.Currently,i have 5 Sets of different Days on it. Why 5 Sets? I make them over the time and store them on 3 different Hardisks.But they are full now and i have to store them elsewhere.And with 70 Bucks for a used Dlt and 5$/Tape,the Cost Issue Disk vs. DLT are no longer valid.The Software i use,is the "famous" Tar from a Linux CD.Why Tar?It just works as it should and no need for a 70$ Backup Software. |
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