zhack.1

ZHACK(1) General Commands Manual ZHACK(1)

zhacklibzpool debugging tool

This utility pokes configuration changes directly into a ZFS pool, which is dangerous and can cause data corruption.

zhack feature stat pool
List feature flags.
zhack feature enable [-d description] [-r] pool guid
Add a new feature to pool that is uniquely identified by guid, which is specified in the same form as a zfs(8) user property.

The description is a short human readable explanation of the new feature.

The -r flag indicates that pool can be safely opened in read-only mode by a system that does not understand the guid feature.

zhack feature ref [-d|-m] pool guid
Increment the reference count of the guid feature in pool.

The -d flag decrements the reference count of the guid feature in pool instead.

The -m flag indicates that the guid feature is now required to read the pool MOS.

zhack label repair [-cu] device
Repair labels of a specified device according to options.

Flags may be combined to do their functions simultaneously.

The -c flag repairs corrupted label checksums

The -u flag restores the label on a detached device

Example:


zhack label repair -cu device
Fix checksums and undetach a device
zhack metaslab leak [-f] pool
Apply a fragmentation profile generated by to the specified pool.

The -f flag forces the profile to apply even if the vdevs in the pool don't have the same number of metaslabs as the fragmentation profile.

The following can be passed to all zhack invocations before any subcommand:

cachefile
Read pool configuration from the cachefile, which is /etc/zfs/zpool.cache by default.
dir
Search for pool members in dir. Can be specified more than once.
var=value
Set the given tunable to the provided value.

# zhack feature stat tank
for_read_obj:
	org.illumos:lz4_compress = 0
for_write_obj:
	com.delphix:async_destroy = 0
	com.delphix:empty_bpobj = 0
descriptions_obj:
	com.delphix:async_destroy = Destroy filesystems asynchronously.
	com.delphix:empty_bpobj = Snapshots use less space.
	org.illumos:lz4_compress = LZ4 compression algorithm support.

# zhack feature enable -d 'Predict future disk failures.' tank com.example:clairvoyance
# zhack feature ref tank com.example:clairvoyance

ztest(1), zpool-features(7), zfs(8)

May 3, 2023 Debian