Begins a scrub or resumes a paused scrub.
The scrub examines all data in the specified pools to verify that it checksums
correctly.
For replicated
(mirror, raidz, or draid)
devices, ZFS automatically repairs any damage discovered during the scrub.
The
zpool
command reports the progress of the scrub and summarizes the results of the
scrub upon completion.
Scrubbing and resilvering are very similar operations.
The difference is that resilvering only examines data that ZFS knows to be out
of date
(
for example, when attaching a new device to a mirror or replacing an existing
device
),
whereas scrubbing examines all data to discover silent errors due to hardware
faults or disk failure.
Because scrubbing and resilvering are I/O-intensive operations, ZFS only allows
one at a time.
A scrub is split into two parts: metadata scanning and block scrubbing.
The metadata scanning sorts blocks into large sequential ranges which can then
be read much more efficiently from disk when issuing the scrub I/O.
If a scrub is paused, the
zpool
resumes it.
If a resilver is in progress, ZFS does not allow a scrub to be started until the
resilver completes.
Note that, due to changes in pool data on a live system, it is possible for
scrubs to progress slightly beyond 100% completion.
During this period, no completion time estimate will be provided.
