Cisco IOS release 12.4(15)T brought (among a plethora of voice features) the logging to non-volatile storage, a nice-sounding name for the ability to write syslog messages into files on your flash memory (or an embedded disk, if you have one). To configure it, use the logging persistent [url directory] [size filesystem-size] [filesize logging-file-size] global configuration command:

• The directory argument specifies where you want the files to be stored (for example, flash:/logging).
• The filesystem-size specifies the maximum disk space the logging files can consume (once you exceed the limit, the oldest file is deleted)
• The logging-file-size parameter specifies the maximum size of each file (once the file grows too large, a new file is created).

Note: You can store the log files on the router's flash memory if it appears as a disk file system (check with the show file systems command). Wouldn't it be great if this feature would also work on USB drives ...