By Paul Raj D. and Bijo S. Kappen
Objective
This paper aims at identifying the software options for
optimum backup performance using HP TurboSTORE/iX with different system
configurations and data patterns.
Using TurboSTORE options
The following are the TurboSTORE options that can be considered
for performance optimization:
- Using high software compression (COMPRESS=HIGH option):
Typically, this option takes about 80% of CPU time on
a single CPU machine for a high-end target device (e.g. DLT8000) and is
CPU intensive. This option gives the best performance when the system load
is very low (e.g. nightly backups when all users/sessions are logged out).
It is recommended not to use this option, if the CPU load is expected to
peak during the backup window. Also, using HIGH compression along with
hardware compression may degrade the backup performance.
- Using low software compression (COMPRESS=LOW option):
Typically, this option takes about 30% of CPU time on
a single CPU machine for a high-end backup device (e.g. DLT8000). To achieve
a better performance, this option can be used along with hardware compression.
On a heavily loaded system, it is recommended to use only hardware compression.
- Interleaving of files on backup (INTER option):
Interleave option gives best performance:
-
when files are evenly distributed across disks.
-
when backup file-set contains many large files.
This option may degrade the backup performance when used
with many small files. Presently TurboSTORE is capable of interleaving
up to four files.
- Using different buffer sizes (MAXTAPEBUF option):
TurboSTORE supports 16KB and 32KB buffer sizes. Default
buffer size is 16KB. For backups to remote devices, only 16KB is supported.
Typically, performance doubles with 32KB buffer (MAXTAPEBUF) when compared
to 16KB.
- Doing parallel backup (STORESET option):
Doing parallel backups helps to reduce the backup window
by several folds, especially on multi-processor systems. When using high-end
devices like DLT8000, a general rule for doing parallel backup is to have
one less target (tape) drive in the parallel set than the number of processors.
For example, on a 4-way system, perform a 3-device parallel backup. This
is because STORE uses two additional processes to control the overall backup.
If you are doing a three device parallel backup, it is possible that you
could get three times the performance of a single backup on a four-way
multiprocessor system.
On a single processor system, one may not see the same
performance improvement with parallel backups. However, depending on the
system configuration, one should still see an increased backup performance.
Optimal h/w configuration
- H/W compression:
Enabling hardware compression alone gives a small percentage
of performance improvement. For best backup performance, it is recommended
to use HIGH software compression, or LOW software compression along with
hardware compression.
- System configuration:
The backup performance not only depends on the backup
software and target drives used, but also on the host machine configuration
and the system load. TurboSTORE creates one process per target drive in
parallel storeset. Hence it is recommended to have one-more processor than
the target drives in the parallel storeset. I.e., on a n-CPU machine its
recommended to have n-1 tape drives. The type of compression should be
selected depending on the CPU load.
- Load balancing:
It is very important to balance the load of each tape
drive during parallel backup. If some tape drives finish their jobs much
earlier than the others do, it does not improve the overall backup performance.
TurboSTORE uses a simple algorithm to divide the files among parallel tape
drives. It stores these files in the sequence they are passed to store
command and never moves them around to balance the loads. It is recommended
to load balance by providing proper mix of files in the fileset if the
backup contains some very large files.
Conclusions
Best performance is achieved with COMPRESS=HIGH and MAXTAPEBUF
options. The HIGH compression option is CPU intensive.
When the CPU load is moderate, it is recommended to use
COMPRESS=LOW and MAXTAPEBUF along with hardware compression.
Proper load balancing with fileset can give best performance
in parallel backup.
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