OpenZFS 7885 - zpool list can report 16.0e for expandsz

Authored by: Steven Hartland <steven.hartland@multiplay.co.uk>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Approved by: Gordon Ross <gordon.w.ross@gmail.com>

When a member of a RAIDZ has been replaced with a device smaller than
the original, then the top level vdev can report its expand size as
16.0E.
The reduced child asize causes the RAIDZ to have a vdev_asize lower than
its vdev_max_asize which then results in an underflow during the
calculation of the parents expand size.
Fix this by updating the vdev_asize if it shrinks, which is already
protected by a check against vdev_min_asize so should always be safe.
Also for RAIDZ vdevs, ensure that the sum of their child vdev_min_asize
is always greater than the parents vdev_min_size.

Reviewed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: George Melikov <mail@gmelikov.ru>
OpenZFS-issue: https://www.illumos.org/issues/7885
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/bb0dbaa
Closes #5963

diff --git a/module/zfs/vdev.c b/module/zfs/vdev.c
index 613a9b51ec837254889d3c946960def9d25d8de6..40293ec1fc10c7a2d72f258eac4c26575aceb894 100644 (file)
--- a/module/zfs/vdev.c
+++ b/module/zfs/vdev.c
@@ -134,7 +134,8 @@ vdev_get_min_asize(vdev_t *vd)
         * so each child must provide at least 1/Nth of its asize.
         */
        if (pvd->vdev_ops == &vdev_raidz_ops)
-               return (pvd->vdev_min_asize / pvd->vdev_children);
+               return ((pvd->vdev_min_asize + pvd->vdev_children - 1) /
+                   pvd->vdev_children);
 
        return (pvd->vdev_min_asize);
 }
@@ -1330,7 +1331,7 @@ vdev_open(vdev_t *vd)
        vd->vdev_psize = psize;
 
        /*
-        * Make sure the allocatable size hasn't shrunk.
+        * Make sure the allocatable size hasn't shrunk too much.
         */
        if (asize < vd->vdev_min_asize) {
                vdev_set_state(vd, B_TRUE, VDEV_STATE_CANT_OPEN,
@@ -1370,12 +1371,21 @@ vdev_open(vdev_t *vd)
        }
 
        /*
-        * If all children are healthy and the asize has increased,
-        * then we've experienced dynamic LUN growth.  If automatic
-        * expansion is enabled then use the additional space.
-        */
-       if (vd->vdev_state == VDEV_STATE_HEALTHY && asize > vd->vdev_asize &&
-           (vd->vdev_expanding || spa->spa_autoexpand))
+        * If all children are healthy we update asize if either:
+        * The asize has increased, due to a device expansion caused by dynamic
+        * LUN growth or vdev replacement, and automatic expansion is enabled;
+        * making the additional space available.
+        *
+        * The asize has decreased, due to a device shrink usually caused by a
+        * vdev replace with a smaller device. This ensures that calculations
+        * based of max_asize and asize e.g. esize are always valid. It's safe
+        * to do this as we've already validated that asize is greater than
+        * vdev_min_asize.
+        */
+       if (vd->vdev_state == VDEV_STATE_HEALTHY &&
+           ((asize > vd->vdev_asize &&
+           (vd->vdev_expanding || spa->spa_autoexpand)) ||
+           (asize < vd->vdev_asize)))
                vd->vdev_asize = asize;
 
        vdev_set_min_asize(vd);