kern/184092: zfs zvol devices are not appearing till after reimport of pool

Tue Nov 19 18:20:00 UTC 2013

>Number:         184092
>Category:       kern
>Synopsis:       zfs zvol devices are not appearing till after reimport of pool
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Nov 19 18:20:00 UTC 2013
>Closed-Date:
>Last-Modified:
>Originator:     Christopher Harrison
>Release:        FreeBSD 9.2-RELEASE amd64
>Organization:
Great Lakes SAN
>Environment:
System: FreeBSD ws.glsan.com 9.2-RELEASE FreeBSD 9.2-RELEASE #0 r255898: Thu Sep 26 22:50:31 UTC 2013 root at bake.isc.freebsd.org:/usr/obj/usr/src/sys/GENERIC amd64
>Description:
cloned zvol's from snapshots do not appear in dev tree.

When creating a zfs volume and snapshoting this volume the volume and snapshot appear just fine in the /dev tree (under /dev/zvol/...).   However, when creating a clone of a snapshot, the dev tree is not updated with the new clone zvol.   The only way I have been able to have the cloned zvol appear in the dev tree is to completely export the zpool and reimport it.   Once the zpool has been reimported the /dev/zvol clone device appears.

It might be related but deleted zvol snapshots also remain and continue to appear in the zvol dev tree after the zvol snapshot has been deleted.
>How-To-Repeat:
create zfs zvol volume
snapshot the zvol volume
create a clone from the zvol volume snapshot
try to access the zvol device from the zvol device tree under /dev/zvol/<poolname>/<zvol>
No device exists
Export the zpool (zpool export <poolname>)
import the zpool (zpool import <poolname>)
The zvol device now appears under the device tree in the proper /dev/zvol area.
>Fix:
Pure speculation at this point:   

update the zfs clone code to check if the cloned dataset is a volume and create a new zvol device if the clone is a volume from the snapshot.

clean/reindex the zvol dev tree when zvol snapshots are destroyed or cloned

>Release-Note:
>Audit-Trail:
>Unformatted: