This statistic shows SFTP bytes/sec requested by clients to the appliance. Various useful breakdowns are available: to show the client, user and filename of the SFTP requests.
See Protocol: FTP bytes for an example of a similar statistic with similar breakdowns.
SFTP bytes/sec can be used as an indication of SFTP load, and can be viewed on the dashboard.
The best way to improve performance is to eliminate unnecessary work, which may be identified through the client, user and filename breakdowns, and the filename hierarchy view. It may be best to enable these breakdowns for short periods only: the by-filename breakdown can be one of the most expensive in terms of storage and execution overhead, and may not be suitable to leave enabled permanently on appliances with high rates of SFTP activity.
These breakdowns can be combined to produce powerful statistics. For example:
"Protocol: SFTP bytes per second for client 'phobos.sf.fishpong.com' broken down by file name" (to view what files a particular client is accessing)
Since SFTP uses SSH to encrypt FTP, there will be additional CPU overhead for this protocol. To check overall CPU utilization of the appliance, see CPU: Percent utilization.