Understanding how fractional reserve affects available space

What fractional reserve provides

Fractional reserve enables you to tune the amount of space reserved for overwrites based on application requirements and the rate of change of your data. You define fractional reserve settings per volume. For example, you can group LUNs with a high rate of change in one volume and leave the fractional reserve setting of the volume at the default setting of 100 percent. You can group LUNs with a low rate of change in a separate volume with a lower fractional reserve setting and therefore make better use of available volume space.

Risk of using fractional reserve

Fractional reserve requires to you actively monitor space consumption and the rate of change of data in the volume to ensure you do not run out of space reserved for overwrites. If you run out of overwrite reserve space, writes to the active file system fail and the host application or operating system might crash. This section includes an example of how a volume might run out of free space when you are using fractional reserve. For details, see How a volume with fractional overwrite reserve runs out of free space.

Data ONTAP provides tools for monitoring available space in your volumes. After you calculate the initial size of your volume and the amount of overwrite reserve space you need, you can monitor space consumption by using these tools. For details, see Chapter 9, Managing Disk Space".

For detailed information

For detailed information, see the following sections: