How the System Restore Tool Handles Hard-Disk Space Usage (300044)

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By default, System Restore is enabled on all hard-disk partitions upon the completion of Windows XP Home Edition and Windows XP Professional Setup. However, after installation of the operating system, System Restore is automatically suspended when there is less than 200 megabytes (MB) of free hard-disk space on the system drive. The service automatically resumes its monitoring activities at the next system idle time -- as soon as 200 MB of hard-disk space is available. The same behavior is expected after Windows XP installation if any of the partitions become low on available hard-disk space.

Additionally, if disk-space use encroaches on the data store size, with non-monitored files for example, System Restore always yields its data store space to the system. This is because the data store size is not a reserved space and is always calculated as effective size. For example, if the data store size is configured to 500 MB, of which 200 MB is already used, and the current free hard-disk space is only 150 MB, the effective size is 350 MB (200 + 150), not 500 MB. In other words, the data store size is always limited by the available free hard-disk space. Specifically, note the following conditions:

• When a given hard disk has less than 80 MB of remaining free disk space, System Restore purges the data store down to 75 percent of its size, or purges at least one restore point (this is the case if the data store is already below 75 percent). System Restore does not stop restore point creation. It continues to create idle time check points as time demands, and keeps purging on a first in, first out (FIFO) basis, as space demands.
• When a disk has less than 50 MB of remaining free disk space, System Restore purges the data store completely and suspends System Restore on all drives (consistent freeze) until the minimum disk space (200 MB) is created again. Then, System Restore restarts monitoring.
  
  NOTE: 200 MB is required on the system drive only.

If any disk is suspended, System Restore is suspended on all disks. If you check the System Restore Properties user interface (UI), it shows the drives as suspended. The reason for this behavior is that, if System Restore performs an independent suspension (freeze), and then you perform a restore, you would restore some drives but not others if the end user did not explicitly disable those drives. This scenario would place the system in a very inconsistent state, especially if you are installing programs on a non-system drive. If you try to start System Restore when it is in the suspended state, you receive the following warning message: When the computer begins to get low on disk space, you receive a pop-out balloon warning in the System Tray (Systray), alerting you that your computer is running low, or is out of, disk space, as the thresholds are approached (which are 200 MB, 80 MB, and 50 MB, respectively). If you click the balloon, the Disk CleanUp utility (DCU) is automatically started in an attempt to free up additional disk space. If the space freed is not sufficient, you receive one of the warning messages listed in the following sections of this article. At that point, you have the opportunity to start the Add/Remove Programs utility to uninstall some programs and create more space on the hard disk.

You receive "low disk space" warning messages from Disk Cleanup when your disks become low on space and System Restore protection is at risk. If you choose to ignore the messages at the 200 MB threshold and become critically low on disk space, you will continue to receive the messages and warning messages at approximately 80 MB and 50 MB of free disk space.

On non-system drives, you receive the warning, but not the additional warnings, after starting DCU.

Balloon Messages

You will receive various balloon messages regarding disk space. These include the following.

At 200 MB of free disk space: At 80 MB and 50 MB of remaining free disk space:

Warning Messages

You will receive various warning messages regarding disk space. These include the following.

At 200-MB threshold of free disk space:

At 80-MB threshold of free disk space:

Note If the system reaches less than 80 MB of free hard-disk space, and you try to start System Restore, you receive the following message: At the 50-MB threshold of free disk space:

Note If you ignore the warning, the next time that you try to start System Restore, you receive the following message: For additional information about the System Restore utility, click the following article numbers to view the articles in the Microsoft Knowledge Base: