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An organization currently using tape backups takes one full backup weekly and incremental
backups daily. They recently augmented their tape backup procedures with a backup-to- disk
solution. This is appropriate because:

fast synthetic backups for offsite storage are supported.

backup to disk is always significantly faster than backup to tape.

tape libraries are no longer needed.

data storage on disks is more reliable than on tapes.

Disk-to-disk (D2D) backup should not be seen as a direct replacement for backup to tape; rather,
it should be viewed as part of a multitiered backup architecture that takes advantage of the best
features of both tape and disk technologies. Backups todisks are not dramatically faster than
backups to tapes in a balanced environment. Most often than not there is hardly a difference, since
the limiting components are not tape or disk drives but the overall sustained bandwidth of the
backup server’sbackplane. The advantage in terms of speed is in restoring performance, since all
data are on hand and can be accessed randomly, resulting in a dramatic enhancement in
throughput. This makes fast synthetic backups (making a full backup without touching the host’s
data only by using the existing incremental backups) efficient and easy. Although the cost of disks
has been reduced, tape-based backup can offer an overall cost advantage over disk-only solutions.
Even if RAID arrays are used for D2Dstorage, a failed drive must be swapped out and the RAID
set rebuilt before another disk drive fails, thus making this kind of backup more risky and not
suitable as a solution of last resort. In contrast, a single tape drive failure does not produceany data
loss since the data resides on the tape mediA. In a multidrive library, the loss of the use of a single
tape drive has no impact on the overall level of data protection. Conversely, the loss of a disk drive
in an array can put all data at ri

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