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Dell ActiveArchive™ 6-3
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 for the cache file.
NOTE: You cannot take a persistent image of the operating system drive (C:).
Cache Thresholds
The Dell ActiveArchive software has two thresholds that provide warnings when the cache
file is approaching maximum capacity. The Cache Full Warning Threshold logs an event in
the event log and displays an error in the NAS Manager status indicator when the cache file
reaches the threshold (default is 80% full). The Cache Full Threshold, which is labeled
Begin deleting images in the NAS Manager, specifies the threshold where the PowerVault
NAS Manager deletes the oldest persistent images with the lowest retention weights until
the cache file is below the Cache Full Threshold (default is 90% full).
Persistent Image Retention Weights
When the system reaches the cache full threshold, the system starts deleting files
depending on the retention weight and age of the persistent image. The system first looks
for the persistent image with the with the lowest retention weight in the cache file and
deletes the oldest persistent image with that retention weight. After all persistent images
with that lowest retention weight have been deleted, Dell ActiveArchive looks for and
deletes the oldest files with the next higher retention weight.
Persistent Image Considerations
When using persistent images, system performance may be degraded, depending on the
rate your data is changing and the number of persistent images kept for each virtual disk.
Read performance of the virtual disk remains constant, regardless of the presence of
persistent images. Read performance of the persistent image is identical to that of the
virtual disk. Write performance, however, may vary. Each initial write to a virtual disk area
causes the Dell ActiveArchive software to rewrite the data to the persistent image cache file,
and the initial write is slower if the data is being protected by a persistent image. Changes
to data that is not protected by a persistent image will not cause a performance degradation.
NOTICE: If you use the
Reinstallation
CD to reinstall your operating system, your persistent
images will be deleted.