Windows Performance through VSS Cleanup and Preassociation

article #1004, updated 73 days ago

These steps can improve Windows performance a whole lot. It works because a vast array of different applications and services in Windows utilize VSS on their backends. Start an administrative CMD, and then…

Step 1:

First we run the following in an administrative CMD:

vssadmin Delete Shadows /All

If there are orphan shadows, you will be asked whether you want to delete them. If there are and you delete them, you will see immediate performance benefit. Reportedly, Windows autodeletes them only after there are 64 per volume. We prefer to see zero!

Step 2:

We now improve any existing preassociation of disk space for VSS. On some machines, this will increase performance very impressively, immediately. In general it keeps them smooth and stable and prevents hesitations. This does not reserve or take up the space, it just “associates” it, makes it ready for use, so that whenever Windows wants to do any of the bajillions of things it does with VSS, things ranging from tiny to enormous, it can skip that step.

It is worthwhile to know that C: on all workstation installs and many server installs, has a minimal preassociation already set up. So this first step is to resize the existing association.

Do the below in administrative CMD:

vssadmin Resize ShadowStorage /For=C: /On=C: /MaxSize=20%

Do repeat for any other active hard drive partitions, D:, E:, et cetera. Don’t worry if you get an error, the next step covers it.

Step 3:

It may well throw an error, saying there is no such association. If this is a workstation OS, vssadmin lacks two commands on workstation OSes which we need to improve further, so in that case we are done. But on any Windows Server OS from 2003, if the error was thrown, we do an Add for every RAID volume:

vssadmin Add ShadowStorage /For=E: /On=E: /MaxSize=20%

Step 4:

And finally (server only), one more thing which can help if, for instance, C: is almost full but E: has plenty of space:

vssadmin Delete ShadowStorage /For=C: /On=C:
vssadmin Add ShadowStorage /For=C: /On=E: /MaxSize=20%

This maximizes overall performance, and also prevents possible backup failures and other issues due to insufficient disk space on C:.


On some machines, the volumes do not have letters. For these you will need to use the volume GUID path. In vssadmin list shadowstorage, they look like this:

Shadow Copy Storage association
   For volume: (\\?\Volume{99ac05c7-c06b-11e0-b883-806e6f6e6963}\)\\?\Volume{99a
   Shadow Copy Storage volume: (\\?\Volume{99ac05c7-c06b-11e0-b883-806e6f6e6963}
   Used Shadow Copy Storage space: 0 B (0%)
   Allocated Shadow Copy Storage space: 0 B (0%)
   Maximum Shadow Copy Storage space: 32 MB (32%)

For such a situation, substitute \\?\Volume{99ac05c8-c06b-11e0-b883-806e6f6e6963} (the whole long string) for C: in the above command lines.

PowerShell will give GUI paths for all volumes thusly:

GWMI -namespace root\cimv2 -class win32_volume

References are here:

Categories:   VSS   Performance