Quote:
Originally posted by jennycards
Hard drives have a higher failure rate than tapes? Hard drives are slower than tapes? WTF are you telling those people???
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The truth, both from research, and my 10 years of experience as a systems administrator.
Hard drives are slower than tapes for restores and full backups because of the nature of hard drives. People don't believe it, but if you understand how magnetic media works, it' becomes clear :
Hard drives do not write data sequentially, and file systemse DEFINATELY do not write data sequentially. This means for large restores and backups, and retrieval/writing of lots of small files, the head on a hard drive has to move around a LOT. It might be somewhat faster for in dividual file restores, but that's it. Hard drives also have a lot more moving parts than a tape.
Tape drives write and read data in sequential blocks, which means large writes and reads, or reads and writes of large numbers of small files, are a lot quicker. Because tapes write sequentially, they use space better as ell, where hard drives are limited by sector size. There is no seek time because it is a dumb "read block 1, readblock 2, read block 3" ..
If your hard drive writes in 1k blocks, a 50byte file and a 1020 byte file will both take 1 block, which is pretty damned inefficient.
I proved this to a rather moronic CEO I used to have to deal with, who claimed it was more efficient to deal with the loss of 1/2 of one hard drive per week in a very large backup raid, instead of having 4 tape drives. His method was to backup to a large (30 disk) raid 10 once a week and switch it with another one. Which meant moving raids back and forth, which meant an average of 1/2 of one failed disk a week. It all works out in the numbers when you do the statistics of a hard drive's mtbf and divide that statistic between the number of drives.