this write had no competition from other disk requests so the disk heads will
have minimal movement across the disk platter regions.
One final performance result of interest is that in our scenario, mirroring
always
degraded performance, even when it was tuned for optimal performance. This is
not surprising since every logical write request is translated into two physical
write operations. However, you may obtain different results in another
environment, particularly if your test is based on a read rather than a write
operation, which we did not investigate here.
8.4 Managing Backup and Restore
It is critically important that a systems administrator both implements and
understands a reliable backup and recovery policy. This section shows you an
example of how to use the volume group backup utilities to save and recover
your system, if your data or configuration information is damaged beyond a
practical repair timeframe.
In particular, the examples in this section will describe:
How to save the contents and configuration of the perfvg volume group.
How to restore the contents and configuration of the perfvg volume group.
How to use the mksysb command to save an image of the volume group.
How to choose some of the storage management related installation options
to reinstall this rootvg image.
244 AIX Storage Management
Suggestion - One image
You should usually place one volume group image on one tape when you use
the smit defaults. This is what you may want to use as a simple backup rule.
Usually, volume groups will be several gigabytes large if they contain two to
three physical volumes, so each volume group will thus usually require at
least one tape cartridge. Also note that the smit fields that you see when you
execute
smitty savevg:
Only allow you to enter the name of
one
volume group in the VOLUME
GROUP to back up field.
Do not allow you to specify a particular image on the backup device.
However, you may be able to get around this by using the
tctl command and
the no-rewind tape device name as in the following sequence from the
command line:
# savevg -i -f′/dev/rmt0.1′ ′availvg
# savevg -i -f′/dev/rmt0.1′ ′perfvg
# tctl -f/dev/rmt0 rewind
# restore -Tvf/dev/rmt0.1
# restore -Tvf/dev/rmt0.1
This seemed to work fine, but is not fully investigated in this example.
If you have a number of small machines attached to a server that has a large
capacity tape drive, then you may decide to use disk space on the server as
a temporary storage area for all your volume group images from the smaller
machines until you back them up.
You must become familiar with the backup and recovery issues and procedures
discussed in:
3.2.1, “Backup/Restore” on page 64.
5.5, “Planning Backup Strategies” on page 89.
AIX Version 4.1 System Management Guide: Operating System and Devices
and
AIX Version 4.1 Installation Guide
.
These books may be in
AIX Version 4.1 Hypertext Information Base Library
on your system. For these examples in particular, you should refer to the
following articles within them.
Backing Up Your System
.
This article appears in both documents at the level of AIX Version 4 that
we used for these examples. Although the articles are very similar, we
found that:
- The version in
AIX Version 4.1 Installation Guide
was easier to follow
to create a rootvg image.
- The version in
AIX Version 4.1 System Management Guide: Operating
System and Devices
had more information regarding how to backup
other volume groups that are part of your system configuration.
AIX Version 4.1 System Management Guide: Operating System and Devices
.
The articles of interest for these examples in this document include:
Chapter 8. Practical Examples 245

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