Migrate ZFS-* message descriptions (#49)

Prerequisite for changing the URLs in the command outputs from
zfsonlinux.org to openzfs.github.io/openzfs-docs/

Signed-off-by: Ryan Moeller <ryan@iXsystems.com>

docs/msg/ZFS-8000-8A/index.rst

@@ -0,0 +1,111 @@
+..
+   CDDL HEADER START
+
+   The contents of this file are subject to the terms of the
+   Common Development and Distribution License (the "License").
+   You may not use this file except in compliance with the License.
+
+   You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+   or http://www.opensolaris.org/os/licensing.
+   See the License for the specific language governing permissions
+   and limitations under the License.
+
+   When distributing Covered Code, include this CDDL HEADER in each
+   file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+   If applicable, add the following below this CDDL HEADER, with the
+   fields enclosed by brackets "[]" replaced with your own identifying
+   information: Portions Copyright [yyyy] [name of copyright owner]
+
+   CDDL HEADER END
+
+   Portions Copyright 2007 Sun Microsystems, Inc.
+
+.. highlight:: none
+
+Message ID: ZFS-8000-8A
+=======================
+
+Corrupted data
+--------------
+
++-------------------------+----------------------------------------------+
+| **Type:**               | Error                                        |
++-------------------------+----------------------------------------------+
+| **Severity:**           | Critical                                     |
++-------------------------+----------------------------------------------+
+| **Description:**        | A file or directory could not be read due to |
+|                         | corrupt data.                                |
++-------------------------+----------------------------------------------+
+| **Automated Response:** | No automated response will be taken.         |
++-------------------------+----------------------------------------------+
+| **Impact:**             | The file or directory is unavailable.        |
++-------------------------+----------------------------------------------+
+
+.. rubric:: Suggested Action for System Administrator
+
+Run ``zpool status -x`` to determine which pool is damaged:
+
+::
+
+   # zpool status -x
+     pool: test
+    state: ONLINE
+   status: One or more devices has experienced an error and no valid replicas
+           are available.  Some filesystem data is corrupt, and applications
+           may have been affected.
+   action: Destroy the pool and restore from backup.
+      see: https://openzfs.github.io/openzfs-docs/msg/ZFS-8000-8A
+    scrub: none requested
+   config:
+
+           NAME                  STATE     READ WRITE CKSUM
+           test                  ONLINE       0     0     2
+             c0t0d0              ONLINE       0     0     2
+             c0t0d1              ONLINE       0     0     0
+
+   errors: 1 data errors, use '-v' for a list
+
+Unfortunately, the data cannot be repaired, and the only choice to
+repair the data is to restore the pool from backup.  Applications
+attempting to access the corrupted data will get an error (EIO), and
+data may be permanently lost.
+
+The list of affected files can be retrieved by using the ``-v`` option to
+``zpool status``:
+
+::
+
+   # zpool status -xv
+     pool: test
+    state: ONLINE
+   status: One or more devices has experienced an error and no valid replicas
+           are available.  Some filesystem data is corrupt, and applications
+           may have been affected.
+   action: Destroy the pool and restore from backup.
+      see: https://openzfs.github.io/openzfs-docs/msg/ZFS-8000-8A
+    scrub: none requested
+   config:
+
+           NAME                  STATE     READ WRITE CKSUM
+           test                  ONLINE       0     0     2
+             c0t0d0              ONLINE       0     0     2
+             c0t0d1              ONLINE       0     0     0
+
+   errors: Permanent errors have been detected in the following files:
+
+           /export/example/foo
+
+Damaged files may or may not be able to be removed depending on the
+type of corruption.  If the corruption is within the plain data, the
+file should be removable.  If the corruption is in the file metadata,
+then the file cannot be removed, though it can be moved to an
+alternate location.  In either case, the data should be restored from
+a backup source.  It is also possible for the corruption to be within
+pool-wide metadata, resulting in entire datasets being unavailable.
+If this is the case, the only option is to destroy the pool and
+re-create the datasets from backup.
+
+.. rubric:: Details
+
+The Message ID: ``ZFS-8000-8A`` indicates corrupted data exists in
+the current pool.