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 type of data that compression and deduplication reduces.

Prerequisites

Data Reduction must be applied to the volume.

Steps

1. If you are connected to a Data Collector, select a Storage Center from the drop-down list in the left navigation pane of Unisphere

Central.

From the

STORAGE menu, click Volumes.

The Volumes view is displayed.

3. In the Volumes view, select the volume you want to modify.

4. Click (Edit).

The Edit Volume dialog box opens.

5. Expand the Data Reduction menu.

6. 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

7. Click OK to close the Edit Advanced Volume Settings dialog box.

8. 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