ZFS Metadata Compression

zfs_mdcomp_disable

Description

This parameter controls compression of ZFS metadata (indirect blocks only). ZFS data block compression is controlled by the ZFS compression property that can be set per file system.

Data Type

Boolean

Default

0

Range

0 (enabled) or 1 (disabled)

Dynamic?

Yes

Validation

No

When to Change

In general, metadata compression should be enabled. For metadata intensive loads, this default is expected to gain some amount of space (a few percentages) at the expense of a little extra CPU computation. However, a bigger motivation exists to have metadata compression on. For directories that grow to millions of objects then shrink to just a few, metadata compression saves large amounts of space (greater than 10 times).

I/O on flash storage devices is aligned along 4 KB boundaries. If metadata compression is enabled, the I/O on flash storage devices might become unaligned. You might consider disabling metadata compression to resolve the I/O alignment problem if you are using flash devices for primary storage. Using separate log devices on flash devices are not effected by the alignment problem.

Commitment Level

Unstable