IBM E16RMLL-I - Tivoli Storage Manager, Implementation Manual, Page: 544 / 828

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IBM Tivoli Storage Manager Implementation Guide
15.6.3 File system volumes versus raw logical volumes
As a rule of thumb, the general recommendation is to put Tivoli Storage Manager
server volumes on
raw logical volumes
(RLV) in a UNIX environment. In addition
to the read/write performance, RLV volumes do not fragment and the creation is
very fast. Support for RLVs is available on all UNIX Tivoli Storage Manager
platforms, with the exception of Linux. RLVs are not supported for sequential
access storage pools (device class of type file).
Tests on AIX have shown little difference in performance between using Tivoli
Storage Manager storage pool volumes on JFS2 file systems using direct I/O
and raw logical volumes. The same is true for tests on Solaris systems using
VxFS file systems with the QuickIO option being enabled.
If you decide to place your server volumes on a file system, be aware of
fragmentation in the file system, especially if you create a lot of volumes at the
same time. Also, creating such volumes can take some time, as the whole file is
written during initialization.
15.6.4 AIX virtual memory system tuning
AIX is very aggressive in caching file system data. In many cases this is highly
desirable. In the case of Tivoli Storage Manager, file system caching provides no
benefit since the data is not likely to be in cache when it is needed (for migration
or restore). This is due to the large volume of data Tivoli Storage Manager
processes, which is typically much greater than available memory.
AIX will often page out application memory (including Tivoli Storage Manager) in
favor of file system cache data. This is undesirable since it often causes the
Tivoli Storage Manager database buffer pool to be paged out to disk, negating
much of the benefit of the buffer pool. This can cause misleading database
cache hit statistics since Tivoli Storage Manager believes it has that data in
memory, when in fact it has much of that data on disk in paging space. The
symptoms for this behavior are high-paging rates, as seen by the
vmstat
command. This can be avoided by tuning AIX such that it will not favor file
system cache over application memory. This is accomplished by using the
vmtune
command provided in the bos.adt.samples AIX fileset.
By default, AIX will use up to 80% of memory as a file system cache. For
machines dedicated to Tivoli Storage Manager this should be lowered. A good
starting point is 50%. This parameter is called maxperm. This may be done by
Note: On AIX, be aware that only storage pool volumes attempt to utilize the
AIXDIRECTIO option, not database or log volumes.