VSS Error EventID: 8193 from the Event Log (Cannot find anymore diff area candidates for volume)


Problem

Sometimes, when you perform a backup, it stops in a few minutes or even right after the start with the following error message: "The provider returned an unexpected error code".

The research of the log files gives more details about this fail and explains the reason behind it:

VSS Error 12/7/2018 8:23:12 AM EventID: 8193 Volume Shadow Copy Service error: Unexpected error calling routine Cannot find anymore diff area candidates for volume \?\Volume{ae7c3d9e-5755-11e1-9069-806e6f6e6963}\ [0]. hr = 0x8000ffff, Catastrophic failure.

Operation: Automatically choosing a diff-area volume Processing EndPrepareSnapshots

Context: Volume Name: \?\Volume{ae7c3d9e-5755-11e1-9069-806e6f6e6963}\ Volume Name: \?\Volume{ae7c3d9f-5755-11e1-9069-806e6f6e6963}\ Execution Context: System Provider

This error means that the system doesn't have enough disk space to create a shadow copy during a backup. You need to increase the area allowed to VSS to buffer such write operations.

The VSS (Volume Shadow Copy Service) is a technology that provides the ability to create a point in time snapshot (or a shadow copy) to perform a backup of one or more volumes even when they are in use.


Suggestions and Solutions

The resolution is quite simple - you need to increase the shadow copy storage area for the volume listed in the error message: \?\Volume{ae7c3d9e-5755-11e1-9069-806e6f6e6963}

To find the value of the affected volume, do the following:

  1. Run Command Propt as Administrator and type the command mountvol which will give you a list of all possible values for the current mount points.

  1. Find the value associated with the volume and than proceed to increase the size of the shadow copy storage area for this volume

All commands below should be run from an administrator command prompt.

  1. To list all existing shadow storage associations use command
vssadmin list shadowstorage 

  1. If the output for the command is "No items found that satisfy the query" - there is no association exists for the needed volume. To proceed, add a shadow storage for that volume manually using the command
vssadmin add shadowstorage /for=<ForVolumeSpec> /on=<OnVolumeSpec> [/maxsize=<MaxSizeSpec>] 

For example, the command which adds the shadow storage area of 200 Gb in size for a 1 Tb volume with a label D will be the following

vssadmin add shadowstorage /for=D: /on=D: /maxsize=200GB
  1. If a shadow storage association already exists you will need to resize the shadow storage area:
vssadmin resize shadowstorage /for=<ForVolumeSpec> /on=<OnVolumeSpec> [/maxsize=<MaxSizeSpec>]

Resizing the storage association may cause shadow copies to disappear.

Note: When no shadow storage association exists for a volume, the shadow copies utility will display 10% of the volume or MinDiffAreaFileSize, whichever is greater. However, Windows may set a different maximum size during shadow copy creation. While the default behavior works well for most volumes, setting a limit of 15-20% of the total volume size may be needed on busy servers.

References:

  1. Vssadmin list shadowstorage
  2. Vssadmin add shadowstorage
  3. Vssadmin resize shadowstorage

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