This article is for Amanda Enterprise
VSS Shadowstorage Space
Zmanda Windows Client, like all VSS-based backup applications, requires space for VSS snapshots on any disk which contains data that is part of a backup. This space is known as shadowstorage. Backups will usually fail if there is not enough shadowstorage space for snapshots.
Manual Shadowstorage Assignment
You may manage shadowstorage manually via the Windows command prompt using the vssadmin commands, as shown in the following Microsoft Knowledge Base article: https://technet.microsoft.com/en-us/library/cc754968.aspx.
Below are examples of how to add or resize shadowstorage manually.
How to Add Shadowstorage Space if None Exists
To add shadowstorage space if none exists, please follow these steps:
Open an elevated command prompt using the run as administrator option.
Enter the command: vssadmin add shadowstorage /for=X: /on=X: /maxsize=10%.
You may substitute any drive letter for X: in the above command. This includes allotting space for one drive on another.
For example, if you entered vssadmin add shadowstorage /for=C: /on=D: /maxsize=10%, then any snapshots for the C: drive would be created on the D: drive. This allows you to allot space for snapshots for any drive, even if a drive does not have enough free space to hold them.
You may also substitute other values for the /maxsize value. Examples include 20%, 10GB, 5000MB, and so on.
The vssadmin add shadowstorage command is described in full on Microsoft’s website at https://technet.microsoft.com/en-us/library/cc788051.aspx.
How to Resize Existing Shadowstorage Space
Please be cautious if you change the Maximum Shadow Copy Storage space. If you lower the amount of space available, Windows will automatically remove any excess snapshots, starting with the oldest. This is most common when the shadowstorage space is changed from UNBOUNDED to some smaller value, but may occur any time the shadowstorage space is reduced.
ZWC itself does not need old snapshots for any reason. Your backups on disk and/or cloud are safe. However, this may not be true for other applications, especially other backup applications. Please consult your system administrator before resizing your shadowstorage.
To resize existing shadowstorage space, please follow these steps:
Enter the command: vssadmin resize shadowstorage /for=X: /on=X: /maxsize=10%.
For example, if you entered vssadmin resize shadowstorage /for=C: /on=D: /maxsize=10%, then any snapshots for the C: drive would be created on the D: drive. This allows you to allot space for snapshots for any drive, even if a drive does not have enough free space to hold them.
The vssadmin resize shadowstorage command is described in full on Microsoft’s website at https://technet.microsoft.com/en-us/library/cc788050.aspx.
How to Verify the Amount of Shadowstorage Space Currently in Use
To verify the amount of shadowstorage space currently in use, please follow these steps:
Enter the command: vssadmin list shadowstorage.
The command will return information on the used, allocated, and maximum shadowstorage space allowed for snapshots.
We are concerned with the Maximum Shadow Copy Storage space value.
Maximum Shadow Copy Storage space must be equal to or be greater than 10% of the drive’s size.
If a drive is not listed, then there is no space allotted for snapshots at all. You must add space for the snapshots.
If the Maximum Shadow Copy Storage space for a drive is lower than 10%, please resize the value to 10%.
If the Maximum Shadow Copy Storage space is equal to or higher than 10%, and you have received any of the common errors above, please resize the value to 20%.
If the Maximum Shadow Copy Storage space is set to UNBOUNDED, you should consider resizing the value to 10% or 20%.
When UNBOUNDED, Windows will never automatically delete old snapshots. These snapshots can fill up the entire drive.