Capacity; Reliability - HP J3278B - SureStore CD-ROM Server/Tower 7 NAS Server User Manual

Capacity

Reliability

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9 2 Backing Up and Restoring Files
Each DAT or DLT tape drive has a nominal capacity that assumes
an estimate of a 2-to-1 compression ratio.
For example, the HP DAT40i has a native capacity of 20 GB.
If the compression of the files you back up on it is actually 2:1,
then 40 GB will fit. Actual compression will vary.
Since each backup on the HD server can use only one tape, you may
not be able to back up the entire file system at a single time. (You
can schedule up to eight different backups, each comprising a
portion of the file system.)
For example, if your server uses six 9-GB disk drives, with the
sixth drive as a spare, the storage capacity of your RAID volume
is approximately 4 times 9 GB, or 36 GB (since RAID 5 uses the
equivalent of one drive for redundancy). A file system that fills
all capacity on the server may therefore fit on a single 40-GB
tape if compression is used and reaches the 2:1 ratio.
If you convert the spare to a sixth drive and fill it, then you
must ensure that you have the tape capacity of 5 (6 drives
minus 1 for RAID) times 9 GB, or 45 GB with enough
compression, before you include the entire file system on one
tape.
Frequent causes of restore failures are blank and damaged tapes.
Another is that the desired file cannot be found on the tape. Some
preventions are the following:
•
Correct handling of the tape on insertion and ejection.
Never use force in inserting cartridges. Place it squarely in the
slot and push it gently in the middle until the mechanism pulls
in the cartridge.
•
Correct storage of the tape.
Heat, condensation, dust, and magnetic fields damage data
cartridges. Put cartridges in their protective cases when
removed from drive. Store away from heat, dust, and magnetic
sources. Do not pile a tape label upon another label.
•
Useful life of the tape.
Consult the documentation for the tape to understand the tape's
useful life. Count usages by repositions of the drive mechanism
on the tape. Consider the humidity as well as the temperature
of your storage environment.