One way to conserve disk space is to compress files. If you set the File Compression attribute for a Traditional volume, NetWare compresses files that have been inactive for a period of time. Compression typically occurs at non-peak hours.
IMPORTANT:You cannot use compression for volumes on removable drives, such as CDs, DVDs, or ISO files.
NetWare maintains the original version of a file during compression. When compression completes, NetWare replaces the original with the compressed version of the file, if no errors occurred. If errors do occur during compression, NetWare leaves the original version intact.
This section discusses the following topics:
To effectively use file compression for your Traditional volumes, you must understand several key concepts:
Files automatically pass in and out of their compressed state as they are unused, then used. It is not necessary to separate application files from data files for file compression because NetWare compresses files based on the interval of time that a file remains inactive. Most application files are used regularly.
Compressed files are uncompressed as they are needed, then remain uncompressed until they are inactive for an extended period. For a file to be uncompressed, there must be enough free space on the volume to accommodate the uncompressed file size.
Compression is usually a low-priority process thread because of compression’s impact on performance. If you flag an item for immediate compression during peak system usage, performance might deteriorate.
Backup applications that use Novell Storage Management Services™ (SMS™) can back up and restore files in their compressed state. Other applications might decompress them.
The File Compression attribute can be turned on when you create the Traditional volume or at any time afterwards. However, after you enable file compression for a Traditional volume, you cannot turn it off. Instead, you can suspend the compression activity, as needed.
If you want to turn off file compression, you must back up the volume in its uncompressed state, then restore the data to a new volume on which the File Compression attribute is not set.
For the NetWare server, the compression parameters apply to all files and directories in compression-enabled volumes on the server. They have no affect on the file compression for volumes where the volume’s File Compression attribute is disabled.
The following list identifies set command parameters that affect file compression. For details about each parameter and instructions for setting them, see NW 6.5 SP8: NSS File System Administration Guide.
Compression Daily Check Stop Hour
Compression Daily Check Starting Hour
Minimum Compression Percentage Gain
Enable File Compression
Maximum Concurrent Compressions
Convert Compressed to Uncompressed Option
Decompress Percent Disk Space Free To Allow Commit
Decompress Free Space Warning Interval
Deleted Files Compression Option
Days Untouched Before Compression
You choose to compress files when you create volumes by setting the File Compression attribute.You can also set the File Compression attribute later. However, after you enable file compression for a volume, you cannot turn it off. For instructions on setting file compression for volumes, directories, and files, see Setting Server-Level File Compression Attributes.
Use the set command’s parameter named to set this interval of inactivity. This parameter specifies the number of days that must pass without access to a file before the file can be compressed. The parameter uses the date the file was last accessed to gauge whether a file should be compressed.
To avoid the overhead of uncompressing files that do not compress well, the system calculates the compressed size of a file before actually compressing it. If no disk space can be saved by compression, or if the size difference does not meet the value specified by the set command’s parameter named , the file is not compressed.
File compression is enabled and disabled at the volume level. If you do not enable the File Compression attribute when you create a volume, you can subsequently enable it using the set command. However, after it is enabled, file compression cannot be disabled on the volume unless you re-create the volume.
You can temporarily suspend file compression using the set command’s parameter. For more information, see Section 5.1.5, Suspending File Compression.
While file compression is suspended, files that would have been compressed are queued and compressed when compression is re-enabled.