Sun Microsystems Virtual Tape Library - Manual (Page 20)

Advantages of VTL tape virtualization
6 VTL User Guide • May 2008 G • 96267
that produce intermittent or non‐sequential I/O, such as incrementals and backups of
work stations, are copied to tape only after they have been backed up to disk and
incorporated into large, sequential backup sets. This approach uses tape drives
continuously, at close to their maximum throughput. The drives spend less time idle,
since they mount and reposition less often. Fewer drives and tapes are needed for a
given workload. Devices and media suffer less wear and tear.
Improved utilization of backup media
Tape virtualization lets you create emulated tape volumes that are more closely sized
to the average size of your backup media. If you do not decide to use tape caching
(see “Automated Tape Caching” on page 12), you set the maximum capacity of your
virtual tapes to 50‐60 GB or to the average size of your backup jobs (whichever is
larger). This approach minimizes wasted space in the critical disk cache, where the
first copy of each backup job is stored, and makes a maximum number of cartridges
available for backup jobs at any given time. Your copy/vault software can then
consolidate these smaller volumes onto full‐sized physical tape cartridges outside
the backup window. If you also enlarge the size of the library, as described below,
you can accomodate a larger total number of these smaller virtual tapes.
If you adopt tape caching, you cannot size virtual tapes this way, since, as we shall
see, the disk and physical‐tape images of the virtual tape must be logically identical.
Larger, more flexible libraries
The Sun VTL virtual library faithfully emulates a Sun L700 physical tape library.
But, while the L700 has 678 slots, the Sun VTL can have up to 64000 in a non‐tape
caching solution, depending on the backup application (see “Automated Tape
Caching” on page 12). This is a particularly important consideration if you improve
media utilization by reducing the size of your virtual tape volumes, as described
above. One large virtual library can, on its own, serve all the needs of a backup
application master server.
Compatibility with ACSLS management software
Tape virtualization lets you control disk‐based virtual libraries with the same
industry‐standard, Sun ACSLS software that controls physical tape libraries. ACSLS
adds an additional virtualization layer to your backup environment, further
reducing disruptions to established infrastructure and policies while, at the same
time, bringing new capabilities.