ZFS ZVOL, snapshots drive and Virtualbox


I have a running system with Virtualbox and one of its disk is a zvol (type dev) attached to it.
To do my backups, I do a snapshot of this zvol on a snapshot drive. For the sake of completeness, I have my source zvol mounted in /dev/zvol/emTank/vmWin/data and my snapshot zvol mounted to /dev/zvol/rsnap/vmWin/data.

ls -als /dev/zvol/emTank/vmWin/data
0 crw-r----- 1 windows windows 0x5a Feb 26 11:35 /dev/zvol/emTank/vmWin/data
ls -als /dev/zvol/snap/emTank/vmWin/data
0 crw-r----- 1 root operator 0xcb Feb 29 07:49 /dev/zvol/snap/emTank/vmWin/data

The issue I am having is that whenever my snapshot drive gets imported, the Virtualbox machine looses control (hangs on disk access) as if there was some overlap happening.

Also, in the logs, I get the following:

ZFS WARNING: Unable to create ZVOL snap/emTank/vmWin/data@zfs-auto-snap_daily-2015-12-15-04h31

Here is the zvol information:

snap/emTank/vmWin/data  type  volume  -
snap/emTank/vmWin/data  creation  Wed Dec 23 10:18 2015  -
snap/emTank/vmWin/data  used  2.53G  -
snap/emTank/vmWin/data  available  2.33T  -
snap/emTank/vmWin/data  referenced  1.02G  -
snap/emTank/vmWin/data  compressratio  1.47x  -
snap/emTank/vmWin/data  reservation  none  default
snap/emTank/vmWin/data  volsize  20G  local
snap/emTank/vmWin/data  volblocksize  8K  -
snap/emTank/vmWin/data  checksum  on  default
snap/emTank/vmWin/data  compression  on  inherited from snap
snap/emTank/vmWin/data  readonly  off  default
snap/emTank/vmWin/data  copies  1  default
snap/emTank/vmWin/data  refreservation  none  default
snap/emTank/vmWin/data  primarycache  all  default
snap/emTank/vmWin/data  secondarycache  all  default
snap/emTank/vmWin/data  usedbysnapshots  1.50G  -
snap/emTank/vmWin/data  usedbydataset  1.02G  -
snap/emTank/vmWin/data  usedbychildren  0  -
snap/emTank/vmWin/data  usedbyrefreservation  0  -
snap/emTank/vmWin/data  logbias  latency  default
snap/emTank/vmWin/data  dedup  off  default
snap/emTank/vmWin/data  mlslabel  -
snap/emTank/vmWin/data  sync  standard  default
snap/emTank/vmWin/data  refcompressratio  1.12x  -
snap/emTank/vmWin/data  written  0  -
snap/emTank/vmWin/data  logicalused  3.08G  -
snap/emTank/vmWin/data  logicalreferenced  1.10G  -
snap/emTank/vmWin/data  volmode  dev  local
snap/emTank/vmWin/data  snapshot_limit  none  default
snap/emTank/vmWin/data  snapshot_count  none  default
snap/emTank/vmWin/data  redundant_metadata  all  default

Anyone can tell me what is happening?



A small update; I'm not sure if it is the fact that the drive is actually there or tne snapshot that it being taken. I modified my scipts to make sure the virtual machine is indeed frozen (or held) before a snapshot is taken.