Dell PowerVault 775N (Rackmount NAS Appliance) - Manual (Page 74)

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Dell ActiveArchive
Dell™ PowerVault™ 77xN NAS Systems Administrator's Guide
Introduction to Persistent Images
Configuring the Persistent Image Global Settings
Configuring Persistent Image Volume Settings
Using Persistent Images
Scheduling Persistent Images
Accessing Stored Persistent Images
Restoring Volumes From an Existing Persistent Image
Reextending an Extended Volume
Changing the Dell ActiveArchive Event Log Language
Defragmenting a Volume Containing Persistent Images
Dell ActiveArchive™ allows the creation and preservation of persistent images of your NAS system's data volumes. The Dell
ActiveArchive software can be configured using the NAS Manager.
Introduction to Persistent Images
A persistent image is a point-in-time copy of a disk volume. A persistent image contains an exact copy of the file system at
the time the persistent image was created. If you change a file on the active file system after taking a persistent image, the
persistent image contains the old version of the file. If an active file gets corrupted or deleted, you can restore the old version
by copying the file from the latest persistent image or restoring the entire volume. Also, because the persistent image
contains the contents of the file system when the persistent image was taken, you can perform a backup from the persistent
image without stopping all I/O to the NAS system, thus eliminating the backup window required by other types of backup.
NOTICE: Persistent images are temporary backups of your data that reside on the same volume as your data. If the
volume becomes damaged and you lose your data, the persistent image is also lost. Therefore, persistent images do
not replace regular backups of your volume.
Cache File
The Dell ActiveArchive software stores changed data in a cache file. A cache file resides on each volume of your system. By
default, the persistent image cache file is 20 percent of each volume. You can use the NAS Manager to change the percentage
of the volume that is dedicated to the cache file.
NOTE: You cannot take a persistent image of the operating system volume.
Cache Thresholds
The Dell ActiveArchive software has two thresholds that provide warnings when the cache file is approaching maximum
capacity. The warning threshold logs an event in the event log and displays a warning in the NAS Manager status indicator
when the cache file reaches the threshold (default is 80 percent full). The deletion threshold, which is labeled "Begin deleting
images" in the NAS Manager, specifies the threshold at which the NAS Manager deletes the oldest persistent images with the
lowest retention weights until the cache file is below the deletion threshold (default is 90 percent full). The NAS Manager
indicates when it is necessary to delete persistent images to get below the threshold by displaying an error on the NAS
Manager Status page.
Persistent Image Retention Weights