ZFS - recovering destroyed pools

If you created zfs pool with filesystems on it - it could happen that you destroyed that pool not really wanting it. Fortunatelly when you destroy a pool all that ZFS does is it marks that pool as 'destroyed' but no data or config on disks are erased. Making some really simple changes to ZFS utils (and to ZFS fs itself) you can easly recover previously destroyed pools with all filesystems and data on them.
When you do 'zfs import' it lists you available pools in a system skipping destroyed pools. After applying below changes you will also see destroyed pools which are marked '(DESTROYED)' in a state property. Using 'zpool import -f ' you can import again such pool.

bash-3.00# zpool create backup c2t0d0p0
bash-3.00# zfs create backup/d1
bash-3.00# zfs create backup/d2
bash-3.00# zfs list
NAME                   USED  AVAIL  REFER  MOUNTPOINT
backup                 376K  37.0G   100K  /backup
backup/d1             98.5K  37.0G  98.5K  /backup/d1
backup/d2             98.5K  37.0G  98.5K  /backup/d2
bash-3.00#

bash-3.00# df -h -F zfs
Filesystem             size   used  avail capacity  Mounted on
backup                  37G    99K    37G     1%    /backup
backup/d1               37G    98K    37G     1%    /backup/d1
backup/d2               37G    98K    37G     1%    /backup/d2
bash-3.00#

bash-3.00# cp -rp /usr/kernel/ /backup/d1/
bash-3.00# cp -rp /usr/platform/ /backup/d2/
bash-3.00#
bash-3.00# df -h -F zfs
Filesystem             size   used  avail capacity  Mounted on
backup                  37G    99K    37G     1%    /backup
backup/d1               37G   3.4M    37G     1%    /backup/d1
backup/d2               37G   849K    37G     1%    /backup/d2
bash-3.00#


bash-3.00# zpool destroy backup
bash-3.00# zpool list
no pools available
bash-3.00#

bash-3.00# zpool import
pool: backup
 id: 6753094033596765985
state: ONLINE (DESTROYED)
action: The pool can be imported using its name or numeric identifier.  The
     pool was destroyed, but can be imported using the '-f' flag.
config:

     backup      ONLINE
       c2t0d0p0  ONLINE
bash-3.00#

bash-3.00# zpool import -f backup
bash-3.00#
bash-3.00# zpool list
NAME                    SIZE    USED   AVAIL    CAP  HEALTH     ALTROOT
backup                 37.2G   4.45M   37.2G     0%  ONLINE     -
bash-3.00# zfs list
NAME                   USED  AVAIL  REFER  MOUNTPOINT
backup                4.42M  37.0G   100K  /backup
backup/d1             3.38M  37.0G  3.38M  /backup/d1
backup/d2              849K  37.0G   849K  /backup/d2
bash-3.00# df -h -F zfs
Filesystem             size   used  avail capacity  Mounted on
backup                  37G    99K    37G     1%    /backup
backup/d1               37G   3.4M    37G     1%    /backup/d1
backup/d2               37G   849K    37G     1%    /backup/d2
bash-3.00#

############################
#Changes to snv_29 source tree.#
############################

bash-3.00$ diff -u lib/libzfs/common/libzfs_import.c.orig lib/libzfs/common/libzfs_import.c
--- lib/libzfs/common/libzfs_import.c.orig      Tue Jan 31 23:51:06 2006
+++ lib/libzfs/common/libzfs_import.c   Tue Jan 31 23:51:58 2006
@@ -547,7 +547,7 @@
             }

             if (nvlist_lookup_uint64(config, ZPOOL_CONFIG_POOL_STATE,
-                   &state) != 0 || state > POOL_STATE_EXPORTED) {
+                   &state) != 0 || state > POOL_STATE_DESTROYED) {
                     nvlist_free(config);
                     continue;
             }
bash-3.00$


bash-3.00$ diff -u uts/common/fs/zfs/vdev.c.orig uts/common/fs/zfs/vdev.c
--- uts/common/fs/zfs/vdev.c.orig       Sat Dec 17 06:15:08 2005
+++ uts/common/fs/zfs/vdev.c    Wed Feb  1 01:24:58 2006
@@ -1147,7 +1147,7 @@
             }

             if (state != POOL_STATE_ACTIVE &&
-                   (!import || state != POOL_STATE_EXPORTED)) {
+                   (!import || (state != POOL_STATE_EXPORTED && state != POOL_STATE_DESTROYED))) {
                     dprintf("pool state not active (%llu)\n", state);
                     nvlist_free(label);
                     return (EBADF);
bash-3.00$


bash-3.00$ diff -u cmd/zpool/zpool_main.c.orig cmd/zpool/zpool_main.c
--- cmd/zpool/zpool_main.c.orig Sat Dec 17 06:16:00 2005
+++ cmd/zpool/zpool_main.c      Wed Feb  1 01:52:58 2006
@@ -799,7 +799,10 @@

     (void) printf("  pool: %s\n", name);
     (void) printf("    id: %llu\n", guid);
-       (void) printf(" state: %s\n", health);
+       (void) printf(" state: %s", health);
+       if (pool_state == POOL_STATE_DESTROYED)
+               (void) printf(" (DESTROYED)");
+       (void) printf("\n");

     switch (reason) {
     case ZPOOL_STATUS_MISSING_DEV_R:
@@ -832,7 +835,10 @@
     if (strcmp(health, gettext("ONLINE")) == 0) {
             (void) printf(gettext("action: The pool can be imported"
                 " using its name or numeric identifier."));
-               if (pool_state != POOL_STATE_EXPORTED)
+               if (pool_state == POOL_STATE_DESTROYED)
+                       (void) printf(gettext("  The\n\tpool was destroyed, "
+                           "but can be imported using the '-f' flag.\n"));
+               else if (pool_state != POOL_STATE_EXPORTED)
                     (void) printf(gettext("  The\n\tpool may be active on "
                         "on another system, but can be imported using\n\t"
                         "the '-f' flag.\n"));
@@ -842,7 +848,10 @@
             (void) printf(gettext("action: The pool can be imported "
                 "despite missing or damaged devices.  The\n\tfault "
                 "tolerance of the pool may be compromised if imported."));
-               if (pool_state != POOL_STATE_EXPORTED)
+               if (pool_state == POOL_STATE_DESTROYED)
+                       (void) printf(gettext("  The\n\tpool was destroyed, "
+                           "but can be imported using the '-f' flag.\n"));
+               else if (pool_state != POOL_STATE_EXPORTED)
                     (void) printf(gettext("  The\n\tpool may be active on "
                         "on another system, but can be imported using\n\t"
                         "the '-f' flag.\n"));
bash-3.00$