MFC r334844, r336180, r336458

r334844

This originated from ZFS On Linux, as
https://github.com/zfsonlinux/zfs/commit/d4a72f23863382bdf6d0ae33196f5b5decbc48fd

During scans (scrubs or resilvers), it sorts the blocks in each transaction
group by block offset; the result can be a significant improvement. (On my
test system just now, which I put some effort to introduce fragmentation into
the pool since I set it up yesterday, a scrub went from 1h2m to 33.5m with the
changes.) I've seen similar rations on production systems.

r336180

Fix up some missed and mis-merges from the sequential scan code
(r334844). Most of the changes involve moving some code around to
reduce conflicts with future merges. One of the missing changes
included a notification on scrub cancellation.

r336458

Fix a couple of typos in r334844 noticed by Richard Kojedzinszky

Approved by: mav
Sponsored by: iXsystems, Inc

MFC r329732: MFV r329502: 7614 zfs device evacuation/removal

illumos/illumos-gate@5cabbc6b49070407fb9610cfe73d4c0e0dea3e77

https://www.illumos.org/issues/7614:
This project allows top-level vdevs to be removed from the storage pool with
“zpool remove”, reducing the total amount of storage in the pool. This
operation copies all allocated regions of the device to be removed onto other
devices, recording the mapping from old to new location. After the removal is
complete, read and free operations to the removed (now “indirect”) vdev must
be remapped and performed at the new location on disk. The indirect mapping
table is kept in memory whenever the pool is loaded, so there is minimal
performance overhead when doing operations on the indirect vdev.

The size of the in-memory mapping table will be reduced when its entries
become “obsolete” because they are no longer used by any block pointers in
the pool. An entry becomes obsolete when all the blocks that use it are
freed. An entry can also become obsolete when all the snapshots that
reference it are deleted, and the block pointers that reference it have been
“remapped” in all filesystems/zvols (and clones). Whenever an indirect block
is written, all the block pointers in it will be “remapped” to their new
(concrete) locations if possible. This process can be accelerated by using
the “zfs remap” command to proactively rewrite all indirect blocks that
reference indirect (removed) vdevs.

Note that when a device is removed, we do not verify the checksum of the data
that is copied. This makes the process much faster, but if it were used on
redundant vdevs (i.e. mirror or raidz vdevs), it would be possible to copy
the wrong data, when we have the correct data on e.g. the other side of the
mirror. Therefore, mirror and raidz devices can not be removed.

Reviewed by: Alex Reece <alex@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: John Kennedy <john.kennedy@delphix.com>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Richard Laager <rlaager@wiktel.com>
Reviewed by: Tim Chase <tim@chase2k.com>
Approved by: Garrett D'Amore <garrett@damore.org>
Author: Prashanth Sreenivasa <pks@delphix.com>

MFC r323355: MFV r323107: 8414 Implemented zpool scrub pause/resume

illumos/illumos-gate@1702cce751c5cb7ead878d0205a6c90b027e3de8
https://github.com/illumos/illumos-gate/commit/1702cce751c5cb7ead878d0205a6c90b027e3de8

FreeBSD note: rather than merging the zpool.8 update I copied the zpool
scrub section from the illumos zpool.1m to FreeBSD zpool.8 almost
verbatim. Now that the illumos page uses the mdoc format, it was an
easier option. Perhaps the change is not in perfect compliance with the
FreeBSD style, but I think that it is acceptible.

https://www.illumos.org/issues/8414
This issue tracks the port of scrub pause from ZoL: https://github.com/zfsonlinux/zfs/pull/6167
Currently, there is no way to pause a scrub. Pausing may be useful when
the pool is busy with other I/O to preserve bandwidth.

Description

This patch adds the ability to pause and resume scrubbing. This is achieved
by maintaining a persistent on-disk scrub state. While the state is 'paused'
we do not scrub any more blocks. We do however perform regular scan
housekeeping such as freeing async destroyed and deadlist blocks while paused.

Motivation and Context

Scrub pausing can be an I/O intensive operation and people have been asking
for the ability to pause a scrub for a while. This allows one to preserve scrub
progress while freeing up bandwidth for other I/O.

Reviewed by: George Melikov <mail@gmelikov.ru>
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed by: Brad Lewis <brad.lewis@delphix.com>
Reviewed by: Serapheim Dimitropoulos <serapheim@delphix.com>
Reviewed by: Matt Ahrens <mahrens@delphix.com>
Approved by: Dan McDonald <danmcd@joyent.com>
Author: Alek Pinchuk <apinchuk@datto.com>

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFV r268119:

4914 zfs on-disk bookmark structure should be named *_phys_t

illumos/illumos-gate@7802d7bf98dec568dadf72286893b1fe5abd8602

MFC after: 2 weeks

MFV r267566:

4390 i/o errors when deleting filesystem/zvol can lead to space map corruption

MFC after: 2 weeks

MFV r254079:

Illumos ZFS issues:
3957 ztest should update the cachefile before killing itself
3958 multiple scans can lead to partial resilvering
3959 ddt entries are not always resilvered
3960 dsl_scan can skip over dedup-ed blocks if
physical birth != logical birth
3961 freed gang blocks are not resilvered and can cause pool to suspend
3962 ztest should print out zfs debug buffer before exiting

MFV r249857:

Merge vendor bugfix for a possible deadlock related to async destroy
and improve write performance by introducing a new lock protecting
tx_open_txg.

Illumos ZFS issues:
3642 dsl_scan_active() should not issue I/O to determine if async
destroying is active
3643 txg_delay should not hold the tc_lock

MFC after: 1 week

Introduce "feature flags" for ZFS pools (bump SPA version to 5000).
Add first feature "com.delphix:async_destroy" (asynchronous destroy
of ZFS datasets).
Implement features support in ZFS boot code.

Illumos revisions merged:
13700:2889e2596bd6
13701:1949b688d5fb
2619 asynchronous destruction of ZFS file systems
2747 SPA versioning with zfs feature flags

References:
https://www.illumos.org/issues/2619
https://www.illumos.org/issues/2747

Obtained from: illumos (issue #2619, #2747)
MFC after: 1 month

Finally... Import the latest open-source ZFS version - (SPA) 28.

Few new things available from now on:

- Data deduplication.
- Triple parity RAIDZ (RAIDZ3).
- zfs diff.
- zpool split.
- Snapshot holds.
- zpool import -F. Allows to rewind corrupted pool to earlier
transaction group.
- Possibility to import pool in read-only mode.

MFC after: 1 month