Administering FlexCache volumes

Viewing FlexCache statistics

Data ONTAP provides statistics about FlexCache volumes to help you understand the access patterns and administer the FlexCache volumes effectively. You can get statistics for your FlexCache volumes using the following commands:

flexcache stats (client and server statistics)
nfsstat (client statistics only)

For more information about these commands, see the na_flexcache(1) and nfsstat(1) man pages.

Client (caching system) statistics

You can use client statistics to see how how many operations are being served by the FlexCache rather than the origin system. A large number of cache misses after the FlexCache volume has had time to become populated may indicate that the FlexCache volume is too small and data is being discarded and fetched again later.

To view client FlexCache statistics, you use the -C option of the flexcache stats command on the caching system.

You can also view the nfs statistics for your FlexCache volumes using the -C option for the nfsstat command.

Server (origin system) statistics

You can use server statistics to see how much load is hitting the origin volume and which clients are causing that load. This can be useful if you are using the LAN deployment to offload an overloaded volume, and you want to make sure that the load is evenly distributed among the caching volumes.

To view server statistics, you use the -S option of the flexcache stats command on the origin system.

Note
You can also view the server statistics by client, using the -c option of the flexcache stats command. The flexcache.per_client_stats option must be set to On.

Flushing files from FlexCache volumes

If you know that a specific file has changed on the origin volume and you want to flush it from your FlexCache volume before it is accessed, you can use the flexcache eject command. For more information about this command, see the na_flexcache(1) man page.

LUNs in FlexCache volumes

Although you cannot use SAN access protocols to access FlexCache volumes, you might want to cache a volume that contains LUNs along with other data. When you attempt to access a directory in a FlexCache volume that contains a LUN file, the command sometimes returns "stale NFS file handle" for the LUN file. If you get that error message, repeat the command. In addition, if you use the fstat command on a LUN file, fstat always indicates that the file is not cached. This is expected behavior.