IBM G27, User Reference

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When you create a persistent image, it appears as a directory on the original drive.
Access rights and permissions from the original drive are inherited by the persistent
image. Persistent images are used in the same way as conventional drives.
However, unlike conventional drives, persistent images are records of the content of
the original drive at the time you created the persistent image. Persistent images
are retained following shutdown and reboot.
There are six PSM tasks in the Disks/Persistent Storage Manager group:
v
Global Settings
v Volume Settings
v Persistent Images
v Schedules
v Restore Persistent Images
v Disaster Recovery
Each of these tasks is described in the following sections. More detailed
descriptions and instructions for each of the control panels and topics are covered
in the online help.
Global Settings
On this panel, you can configure the persistent image system attributes shown in
Table 4.
Table 4. Persistent image global settings
Attribute Default value
Maximum number of persistent images 250
Inactive period 5 seconds
Inactive period wait timeout 15 minutes
Volume Settings
This panel displays statistics for each volume, such as total volume capacity, free
space, and cache file size and usage. You can also select any volume and
configure volume-specific PSM attributes for that volume, as shown in Table 5.
Table 5. Persistent image volume settings
Attribute Default value
Cache-full warning threshold 80 percent full
Cache-full persistent image deletion threshold 90 percent full
Cache size 15 percent (of the total volume
capacity)
Notes:
1. You cannot change the cache size for a volume while there are persistent
images on that volume (the Cache size combination box will be disabled). You
must delete all persistent images on the volume before changing the cache size
for that volume.
2. Cache size (as a percent of volume size) and deletion threshold must be tuned
to meet the heaviest load placed on the system. NAS Gateway 300 appliances
that receive heavy write traffic for sustained periods will correspondingly
generate more cached data per persistent image, as the system preserves old
Chapter 6. Managing and protecting the network and storage
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