Compression levels and defaults

The compression level is a measure of the compression quality. It is expressed as an integer in the range 1 - 9.

Red Hat Enterprise Linux 9.2 LPAR mode z/VM guest KVM guest

Compression quality and performance are conflicting goals. Compression level 1 provides best performance at the expense of quality. Compression level 9 provides the best quality at the expense of performance. The compression level that is provided by the Integrated Accelerator for zEDC is approximately equivalent to level 1.

Acceleration defaults

The following defaults apply to both on-chip acceleration for gzip and zlib in user space and for the kernel zlib:
  • By default, decompression is accelerated.
  • By default, compression is accelerated only if compression level 1 is requested.

Expanding the scope of compression acceleration

Configure software with a configurable compression level to request level 1 to enable on-chip compression.

For other types of software you must configure the on-chip accelerator.
  • Software that hardcodes a compression level other than 1.
  • Software that neither requests a particular level nor provides an option to configure a level. Such software requests level 6 by default.
If level 1 compression is acceptable for your purposes, use overrides to apply on-chip compression to any requested compression level: