compression client option

Compressing the data on the client reduces demand on the network and the IBM Storage Protect server. The reduced amount of data on the server continues to provide performance benefits whenever this data is moved, such as for storage pool migration and storage pool backup. If you use data replication, compressed data remains compressed during the transfer from the source replication server to the target replication server. The data is then stored on the target replication server in the compressed format.

Client compression reduces the performance of each client, and the reduction is more pronounced on the slowest client systems. For optimal backup and restore performance when you have fast clients and a heavily loaded network or server, use client compression. For optimal backup and restore performance when you have a slow client, or a lightly loaded network or server, do not use compression. However, you must consider the trade-off of greater storage requirements on the server when you are not using client compression. The default for the compression option is no.

Compression can cause severe performance degradation if attempts to compress a file fail. Compression fails when the compressed file is larger than the original file. The client detects this size difference and stops the compression process, fails the transaction, and resends the entire transaction uncompressed. Compression failure occurs because the file type is not suitable for compression or the file is already compressed. Short of turning off compression, there are two options that you can use to reduce or eliminate compression failures:

• Use the compressalways yes option. This default option prevents compression reattempts if the compressed file is larger than the uncompressed file.
• Use the exclude.compression option in the client options file. This option disables compression for specific files, for example, all *.gif files or other files that get larger during attempted compression. Excluding these files saves processor cycles because there is no attempt to compress files that cannot be compressed. Look in the client output (dsmsched.log) for files that are causing compression reattempts and exclude those file types.

Do not enable the client compression option if a client has a built-in file compression feature. For example, if hardware compression is in use for the media where Data Protection for Oracle data is stored, do not enable client compression. Compression, on these types of clients, reduces the amount of data that is backed up to the server.

Restriction: Data can be compressed by using NTFS. However, the data must be decompressed before it can be accessed by the IBM Storage Protect server. Therefore, slower backups and higher processor usage might occur if you use NTFS compression.