zhack - libzpool debugging tool

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ZHACK(1) General Commands Manual ZHACK(1)

NAME

zhack — libzpool debugging tool

DESCRIPTION

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

SYNOPSIS

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 zdb 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.

GLOBAL OPTIONS

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

−c cachefile

Read pool configuration from the cachefile, which is /etc/zfs/zpool.cache by default.

−d dir

Search for pool members in dir. Can be specified more than once.

−o var=value

Set the given tunable to the provided value.

EXAMPLES

# 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

SEE ALSO

ztest(1), zpool-features(7), zfs(8) OpenZFS May 3, 2023 ZHACK(1)

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