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How FlexCache volumes share space with other volumes

You can have multiple FlexCache volumes in the same aggregate. You can also have regular FlexVol volumes in the same aggregate as the FlexCache volumes. If you want to set up your system efficiently, you must understand the way these volumes share space.

When you include multiple FlexCache volumes in the same aggregate, each FlexCache volume reserves only a small amount of space. The rest of the space is allocated as required. This means that a "hot" FlexCache volume (one that is being accessed heavily) is permitted to take up more space, while a FlexCache volume that is not being accessed as often will gradually be reduced in size.

Note: When an aggregate containing FlexCache volumes runs out of free space, Data ONTAP randomly selects a FlexCache volume in that aggregate to be truncated. Truncation means that files are removed from the FlexCache volume until the size of the volume is decreased to a predetermined percentage of its former size.

If you have regular FlexVol volumes in the same aggregate as your FlexCache volumes, and the aggregate starts filling up, the FlexCache volumes can lose some of their unreserved space (if it is not being used). In this case, when the FlexCache volume needs to fetch a new data block and it does not have enough free space to accommodate the data block, an existing data block is removed from one of the FlexCache volumes to accommodate the new data block.

If the ejected data is causing many cache misses, you can add more space to the aggregate or move some of the data to another aggregate.