IBM TotalStorage NAS 300 User Reference page 84

v The default size of the cache file per drive is 15 percent of the total drive
v When a shared volume performs a failover operation from one engine in the NAS
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NAS Gateway 300 User's Reference
scheduling any persistent images for that drive, to build the cache file. You can
then delete the persistent image that you just created if you do not need to keep
it.
After the creation of the first persistent image on a volume, future persistent
images on that volume will complete faster.
capacity.
In most cases, that should be sufficient. However, it is possible that it will not be
enough to maintain the number of persistent images that you want to keep
concurrently on the drive, given the amount of file-write activity to the drive. PSM
automatically takes action to prevent the cache file from overflowing, because if
that occurred, PSM would be forced to automatically delete all persistent images
on the drive (when it cannot keep track of changes made to the drive, it cannot
maintain a valid persistent image).
PSM takes the following actions as the cache file usage approaches a full
condition:
– When the cache file usage exceeds the warning threshold (configured in the
PSM Volumes panel for the drive; the default value is 80 percent), PSM
generates a warning message to the system event log (viewable through the
Windows 2000 Event Viewer in the IBM NAS Admin console), and to the alert
log in the Microsoft Windows 2000 for Network Attached Storage user
interface. The name of the source for the message is psman5. Additionally,
while the cache file usage is above the warning threshold, PSM prohibits any
attempt to create a new persistent image, and logs error messages (to the
system log and alert log). The text of the error message that is logged in the
system event log (from psman5) is "A persistent image could not be created
due to error 0xe000102b".
– When the cache file usage exceeds the automatic deletion threshold (also
configured in the PSM Volumes panel for the drive; the default value is 90
percent), PSM automatically selects a persistent image on the volume and
deletes it to reduce the cache file usage. It selects the persistent image with
the lowest retention value (as described in "Persistent Images" on page 64). If
more than one persistent image has the same (lowest) retention value, then
the oldest image will be selected for deletion. If this deletion does not reduce
the cache file usage below the automatic deletion threshold, then it will
continue to select and delete persistent images until the cache file usage is
reduced below the automatic deletion threshold. For each deletion, PSM
generates an error message to the system event log and to the Windows
2000 for Network Attached Storage alert log indicating that a persistent image
was deleted.
You should periodically check the system event log or Windows 2000 for Network
Attached Storage alert log to ensure that the cache file usage is not consistently
high, forcing existing persistent images to be deleted and preventing new
persistent images from being created. If the cache file usage is high, you can
increase the size of the cache file using the PSM Volumes page. However,
because dynamic cache file resizing is not supported in this release, you must
delete all persistent images currently on that volume first.
Gateway 300 to the other engine, the persistent images for that volume move
with the volume. The Persistent Images panel on a particular engine will display
only those persistent images which are on volumes that the engine owns at a
point in time. If persistent images are scheduled for a volume, on a particular