[ERROR] [Shadow Copy] Insufficient storage available to create either the shadow copy storage file or other shadow copy data

Error

The backup log shows the shadow copy being retried, then this error:

[info] [Shadow Copy] (1/10) Will retry in 60 seconds.
...
[info] [Shadow Copy] (10/10) Will retry in 60 seconds.
[ERROR] [Shadow Copy] Insufficient storage available to create either the shadow copy storage file or other shadow copy data.

If there are no open or locked files, a file backup can still complete without the shadow copy. Open or locked files may be skipped, so fix the error even if the backup reports success.

Cause

Windows couldn’t create a shadow copy (VSS snapshot) of the drive. This is usually because:

the drive is low on free space, or
the space Windows allows for shadow copies on that drive is too small, or
the drive has file system errors, even when it has plenty of free space.

Fix

Check that each drive in the backup source has plenty of free space.
Open Command Prompt as administrator (right-click Command Prompt and click Run as administrator) and check how much space shadow copies are allowed:
```
vssadmin list shadowstorage
```
If Maximum Shadow Copy Storage space is small for the drive, increase it, for example to 10% of drive C::
```
vssadmin resize shadowstorage /for=C: /on=C: /maxsize=10%
```
In Event Viewer, check the Application and System logs for disk or VSS errors around the time of the backup.
Check the drive for errors:
```
chkdsk C: /f
```
For the system drive, Windows asks to run the check at the next restart. Type Y, then restart. Add /r for a full scan of the disk surface, which takes much longer.
Restart the server, then run the backup again.

If the error continues, see VSS_E_UNEXPECTED_PROVIDER_ERROR for more VSS checks.

Example

We have seen this error on a server with more than 1TB of free space and no other VSS errors. The Windows event log showed GetVolumeInformation, 0x80070002, The system cannot find the file specified. A full chkdsk and a restart fixed it, and the next backup succeeded.