The following list includes some suggestions to improve performance on busy FTP sites.
Sites which typically support many simultaneous connections should run the FTP server in standalone mode, see Starting the FTP Server Automatically.
Use vmstat and other system utilities to monitor the system hosting the FTP server. If the system runs low on resources place a limit on the number of simultaneous connections, see How to Set User Login Limits. For more information on system monitoring, see Chapter 13, Monitoring System Performance (Tasks), in System Administration Guide: Advanced Administration.
If you impose a connection limit, consider using the limit-time and timeout idle capabilities in the ftpaccess file to stop users from hogging connections. If you don't impose a connection limit, specify the -Q option to in.ftpd.
If you don't need ftp login and logout records in /var/adm/wtmpx, specify the -W option to in.ftpd.
To reduce the load on the system hosting the FTP server, increase the transfer buffer sizes using the recvbuf and sendbuf capabilities in the ftpaccess file. If large buffer sizes are selected it may be necessary to increase the data activity timeout using the timeout data capability in the ftpaccess file.
The FTP server reads from various databases including the hosts, passwd, group and services. Slow lookups may cause a significant delay logging into the FTP server, configuring the files source first in nsswitch.conf minimizes the lookup times. For more information, see the nsswitch.conf(4) man page.
By default the FTP server attempts to lookup the remote host's name, which can be slow causing a significant delay logging in. The rhostlookup capability in the ftpaccess file can be used to stop this lookup. However be aware that if the remote host's name is not looked up, only its IP address is matched when using other capabilities in the ftpaccess file and when matching entries in the ftphosts file. Also the remote host's IP address will be used in messages and in place of the %R magic cookie. See the description of the rhostlookup capability in the ftpaccess(4) man page for more details.
Retrieving quota information may also cause a significant delay when logging into the FTP server, so only use the quota-info capability in the ftpaccess file if you make use of the quota magic cookies. See the ftpaccess(4) man page for a list of the quota magic cookies.