For best caching performance, you should allow Data ONTAP to control the size of your FlexCache volumes, by using the FlexCache Autogrow capability.
Making your FlexCache volume too small can negatively impact your caching performance. When the FlexCache volume begins to fill up, it flushes randomly chosen, previously cached files to make room for newly requested data. When data from the flushed files is requested again, it must be retrieved again from the origin volume.
Therefore it is best to use the Autogrow capability and allow Data ONTAP to increase the size of your FlexCache volumes as the size of the working set increases. This method has the following advantages:
- If the size of the FlexCache volume's working set increases, as long as there is space in the containing aggregate, the FlexCache volume automatically increases its size rather than ejecting data from the cache, which could affect data access performance.
- These size increases happen without operator intervention.
- If you have several FlexCache volumes sharing the same aggregate, the volumes that are getting the most data accesses will also receive the most space.
- If you increase the size of an aggregate, the FlexCache volumes contained by that aggregate will automatically take advantage of the extra space if needed.
The Autogrow capability is enabled by default in new FlexCache volumes created without specifying a size using Data ONTAP 7.3 and later. You can enable the Autogrow capability on existing FlexCache volumes by using the vol options command with the flexcache_autogrow option.
Note: Before the Autogrow capability was available, the preferred sizing strategy for FlexCache volumes was to size the FlexCache volume to the same size as its containing aggregate. If this approach is providing you with the performance and space utilization you need, you do not need to reconfigure those existing FlexCache volumes to use the Autogrow capability.