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Tivoli Storage Manager copy volumes must have at least the same capacity as
the original volumes. If your database consists of eight volumes of 1 GB each,
you will need eight more 1 GB allocated volumes to completely mirror the
database. If you create volumes larger than necessary, Tivoli Storage Manager
gives a warning message (ANR2253W for database and ANR2273W for the log),
but still allows you to use the allocated volume. The extra capacity will be
wasted). We recommend creating all copies of each volume at the same size.
You should mirror all or none of the volumes—there is no point in only mirroring
some of them.
Use separate disks for each of the volumes in a mirrored set, so that you do not
lose data if one disk fails. Although you can technically place primary and mirror
copies on the same disk, this is also a waste of space and will probably even
decrease performance because of disk head contention.
When using two-way mirroring, we recommend using four disks for the database
and recovery log volumes to keep each set of volumes on a separate disk. If you
can, go one step further and ensure that the disks are on separate controllers. In
a SAN environment, your disks will probably be virtualized, and running separate
controllers for each LUN is not likely.
Table 5-1 shows an example of database and recovery log directories for
UNIX/Linux and Windows, respectively. We assume that the four UNIX/Linux file
systems are built on separate disks.
Table 5-1 Database and recovery log volume placement on four disks
Type of volume
Database volumes
Mirrored database volumes
Log volumes
Mirrored log volumes
If four separate disks for your database and recovery log volumes are not
possible, we recommend a minimum of two separate disks. In this way, you can
place primary database and mirror log volumes on one disk, and primary log and
204
IBM Tivoli Storage Manager Implementation Guide
UNIX file system
mount points
/tsm/database/primary
/tsm/database/mirror
/tsm/log/primary
/tsm/log/mirror
Windows location
D:\TSMDATA\DBP
E:\TSMDATA\DBM
F:\TSMDATA\RLP
G:\TSMDATA\RLM
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