Checking and adjusting VSS thresholds

VSS (Volume Shadow Copy Service, sometimes called Volume Snapshot Service), is a technology included in the Microsoft Windows server operating system that allows taking manual or automatic backup copies or snapshots of computer files or volumes. VSS captures and copies stable images for backup on running systems, particularly servers, without unduly degrading the performance and stability of the services they provide.

A VSS threshold is set to limit the amount of disk space used by VSS. It is important to have this threshold set to a sensible limit (recommended at 15% to 20% of total drive capacity). If "no-limit" is selected, then VSS will continue to use more and more of the available drive space until all drive space is used up, at which point applications start to fail due to insufficient drive space.

If there are issues with Cloud Direct backup operation, and VSS errors are indicated in the backup log report, then you should check, and if necessary adjust, the VSS thresholds.

When checking and adjusting VSS thresholds, the following stages, described in this article, should be carried out in this sequence:

• Checking VSS thresholds
• Clearing down VSS memory use
• Creating a new VSS threshold

Important Note:
As part of the Microsoft Windows server operating system, VSS is not a product provided by Cloud Direct. This article is intended as a first step to help resolve VSS related issues affecting Cloud Direct's backup service. However, should VSS-related problems persist then please contact your local IT Support.

Prerequisite

Before commencing this task, you must have details of the total capacity (used, plus unused, space) of each disk drive configured on this Windows computer. Use this information to determine the correct VSS threshold setting for each drive. This should be between 15% and 20% of total drive capacity. For example, a hard drive of total capacity 99.9GB should have a VSS threshold setting of between 15GB and 20GB. Calculate, and make a note of, the recommended VSS thresholds for each of the hard drives that will be backed up on your Windows server.

Checking VSS thresholds

To check the VSS threshold settings, proceed as follows.

1. Open My Computer.

2. Right-click on any of the listed Hard Disk Drives and, from the drop down menu options, click on Configure Shadow Copies.

3. If a window appears, asking you to allow changes, then click Yes.

The Shadow Copies page opens.

The Shadow Copies page lists all drives, or Volumes, on the server.

4. From the list, ensure that any drives you are backing up have Next Run Time set to Disabled. (If not, then select the drive and click the Disable button).
5. Select the first drive in the list, and click the Settings button.

The Settings page, for the selected drive, opens.

From here, you can see the current VSS threshold setting for this drive. In the example above the VSS threshold is 10239MB. Note that this limit applies only if the Use limit radio button is selected.

Note:
A common cause of VSS-related issues is the Maximum size set to No limit. If No limit is selected, then VSS will continue to use more and more of the available drive space until all drive space is used up, at which point applications start to fail due to insufficient drive space.

Clearing down VSS memory use

Continuing from the previous section, Checking VSS thresholds, clear down the VSS memory use as follows.

1. In the Storage area section, ensure that the Maximum size radio button is set to Use limit, then use the up/down arrows in the adjacent box to set the limit at 350MB.
2. Click OK.

The Shadow Copies page re-appears.

3. On the Shadow Copies page, ensure the same drive is selected, then click the Create Now button, to create a shadow copy for this drive.

A shadow copy is created, and indicated in the Shadow copies of selected volume section.

4. Delete the new shadow copy by highlighting it in the Shadow copies of selected volume section, then clicking the Delete Now button.

A confirmation box appears asking if you are sure you want to delete the selected shadow copy.

5. Click Yes.

The shadow copy is deleted, so clearing down the cache.

6. Repeat from Step 5 of Checking VSS thresholds to this point, for all drives that you are backing up on this computer.

Creating a new VSS threshold

Continuing from the previous section, Clearing down VSS memory use, create a new VSS threshold as follows.

1. From the Shadow Copies page, select the required drive, and click the Settings button.

The Settings page, for the selected drive, opens.

2. In the Storage area section, ensure that the Maximum size radio button is set to Use limit, then use the up/down arrows in the adjacent box to set the limit to between 15% and 20% of the total drive capacity. (As noted in the Prerequisite section of this article).
3. Click OK.

The Shadow Copies page re-appears.

4. Click OK to leave the Shadow Copies page.
5. Repeat Step 1 to Step 4 for each drive that you are backing up on this computer, requiring a new VSS threshold.

Note:
This action does not require a reboot in order to take effect.