Hyper-v Backups fail with status 156:snapshot creation failed.

Problem

Hyper-v Backups fail with status 156:snapshot creation failed.

Error Message

Status Code: 156

Solution

1.Log on to the VM for which the backup fails

2.Open My Computer >Right click any drive >click shadow copies

(In server 2008,Right click the drive and select 'configure shadow copies')

3.Select a drive >click settings >Make sure that the storage area for the shadow copy resides on the same volume and the limit defined is at least 10% or more of the used space  on the drive.

This can be done from the command line as well

vssadmin List ShadowStorage

Output will be something like this ,will include all volumes

Shadow Copy Storage association
For volume: (C:)\\?\Volume{578b3fef-0d72-11dc-be49-806e6f6e6963}\
Shadow Copy Storage volume: (C:)\\?\Volume{578b3fef-0d72-11dc-be49-806e6f6e6963}\
Used Shadow Copy Storage space: 89.724 GB
Allocated Shadow Copy Storage space: 89.951 GB
Maximum Shadow Copy Storage space: UNBOUNDED


This shows that the shadow copy storage is on the same drive because the volume is C:\ and the shadow copy storage volume is also C:\

If it is not on the same drive then we can use this command to set it on the same drive

First delete the shadowstorage set on different volume

vssadmin delete shadowstorage /for=<ForVolumeSpec> /on=<OnVolumeSpec> [/quiet]

e.g. vssadmin delete shadowstorage /for=C: /on=D: /quiet

Now add it

vssadmin add shadowstorage /for=<ForVolumeSpec> /on=<OnVolumeSpec> [/maxsize=<MaxSizeSpec>]

vssadmin add shadowstorage /for=C: /on=C: /maxsize=5GB

Here the mxsize should be at least 15% of the used space on the drive

leave out MaxSize parameter, and the max will be set to unbounded.
 

4.Retry the backup