Each switch that will reduce backup time will be because it reduces the
backup error detection & recovery features. The switches that
fall into that category are: /NOCRC /GROUP=0 /NOVERIFY /BLOCK=65535
Other things that might help during backup but make it much harder to
restore is /PHYSICAL
The most important thing in improving backup performance is actually
process tuning. See the VMS Version 5.2 New Features Manual,
AA-LA97B-TE, page 2-15 through 2-17. It has the best backup tuning
hints ever published. Beware that a well tuned BACKUP can saturate
your I/O sub-system, and other users might be negatively impacted.
It can also bring out hardware configuration glitches.
UAF Meaning Recommended
Parameter Value
----------------------------------------------------------------------
WSQUOTA The number of pages of memory the Equal to SYSGEN
working set of the process can parameter WSMAX
consume.
WSEXTENT The absolute limit of physical memory Equal to
allowed to the process. WSQUOTA
NOTE: BACKUP bases its memory
consumption on the WSQUOTA
value, not WSEXTENT.
PGFLQUO The number of pages of memory your Greater than
process is allowed in the page file. or equal to
WSEXTENT up to
VIRTUALPAGECNT
FILLM The number of files that can be open Equal to
simultaneously. BACKUP scans this the SYSGEN
number of files at one time. parameter
CHANNELCNT-15
DIOLM The number of direct I/O operations Maximum of
(usually disk operations) that can be either (3 x
outstanding simultaneously. FILLM) or 4096
ASTLM The number of asynchronous system Maximum of
traps that can be queued to the either (3 x
process simultaneously. FILLM) or 4096
Never lower than
DIOLM
BIOLM The maximum number of buffered I/O Less than or
operations that can be outstanding equal to FILLM
simultaneously.
BYTLM The total number of bytes of memory Greater than
that can be outstanding for buffered or equal to
I/O operations. the following
value: (256 x
FILLM) + (6 x
DIOLM)
ENQLM The maximum number of locks that can Greater than
be queued simultaneously. FILLM
The following table lists a set of UAF parameter values that may be
useful for your configuration:
UAF Parameter Value
--------------------
WSQUOTA 16,384
WSEXTENT Greater than or equal to WSQUOTA
PGFLQUO 32,768
FILLM 128
DIOLM 4,096
ASTLM 4,096
BIOLM 128
BYTLM 65,536
ENQLM 256
You can choose to set the values for WSQUOTA and FILLM lower than
these values under the following circumstances:
o If your disks are highly fragmented, lower values prevent
BACKUP from becoming highly CPU-intensive.
o If you use BACKUP during periods of heavy system use,
lower values prevent BACKUP from consuming too many
system resources.
NOTE: If you decrease the values of UAF parameters other than
WSQUOTA and FILLM, use the ratios in the first table in
this article to determine appropriate values.
