Administrator Guide

Data Eligible for Data Reduction
To reduce the impact of Data Reduction on read and write operations, a limited amount of data is eligible for compression and
deduplication. Data Reduction Input limits the type of data that is eligible for Data Reduction. The following options are available for
Data Reduction Input.
• Inaccessible Snapshot Pages – Allows Data Reduction to process data frozen by a snapshot and made inaccessible by new
data written over the original data in the snapshot.
• All Snapshot Pages – Allows Data Reduction to process data frozen by a snapshot.
Change the Data Reduction Input
Change the Data Reduction Input for a volume to change the type of data that compression and deduplication reduces.
Prerequisites
Data Reduction must be applied to the volume.
Steps
1. Expand the Dell Storage Manager menu, and then click Storage.
2. In the SC Series tab, select a Storage Center to open the Storage Center view.
3. Click the Storage tab.
4. In the Storage tab navigation pane, select a volume.
5. Click Edit. The Edit Volume dialog box opens.
6. Click Edit Advanced Volume Settings.
The Edit Advanced Volume Settings dialog box opens.
7. From the Data Reduction Input drop-down menu, select a Data Reduction input.
• Inaccessible Snapshot Pages – Data frozen by a snapshot that has become inaccessible because other data has been
written over it
• All Snapshot Pages – Data frozen by a snapshot
8. Click OK to close the Edit Advanced Volume Settings dialog box.
9. Click OK.
Compression
Compression reduces the amount of space used by a volume by encoding data. Compression runs daily with Data Progression. To
change the time at which compression runs, reschedule Data Progression. Compression does not run with an on-demand Data
Progression.
When compressed data is read, it is temporarily uncompressed in memory until the read is complete. When compression is disabled,
pages are permanently uncompressed during the next compression cycle, and the original compressed page is deleted as time and
resources permit. When a volume is deleted or a snapshot is coalesced, the related compressed data is also deleted.
Deleted data might create gaps in the compressed page, which can be filled with new compressed data. In addition, compressed
pages are defragmented during Data Progression to remove gaps and use space more efficiently.
The Compression Savings amount is determined by comparing the total amount of space saved from all compressed pages to the
total amount of used space that is eligible for compression. For example, if compression saves 1 GB on a volume with 10 GB of used
space that is eligible for compression, the amount saved is 10 percent.
Apply Data Compression to a Volume
Apply Data Compression to a volume to reduce disk space usage for that volume.
1. Expand the Dell Storage Manager menu, and then click Storage.
2. In the SC Series tab, select a Storage Center.
3. Click the Storage tab.
4. In the Storage tab navigation pane, select a volume.
5. Click Edit. The Edit Volume dialog box opens.
Storage Center Administration
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