Handbook

backup capacity, it can have a significant impact on overall perfor-
mance.The system incorporates software algorithms that select
which files are backed up to the disk portion of the backup space.
In general, the most active files are backed up to disk.Then as these
files become less active,they are migrated to tape backup.Thus,
with a relatively small investment in hard disk storage, system man-
agers can use virtual tape to deal with ever smaller backup win-
dows,without disrupting established, reliable backup processes.
RAIT
When data transfer rate is your number one concern, and down-
time or lost data must be avoided at all costs,you might want to
consider a tape RAIT system (see Figure 9-3).
HORIZONTAL APPLICATIONS9.8
Parity
data data data data
data
Parity data data data
data
data Parity data data
data
data data Parity data
data
data data data Parity
Host
Parallel Data
Queue
Tape
RAIT set
Disk
RAID set
Figure 9-3 RAIT (Redundant Array of Independent Tape drives)
provides many of the same benefits as RAID, but on less costly
and more portable media.