This depends on a few things such as the logging level set (how verbose the logs are) and how busy your server is. Additionally the default number of log files almost always can be increased if you want to be able to save more logs on the server itself. To figure out how many logs you can save look at the CCM trace setting or whatever service you're interested in, look at the number of files and size per file. Then use a "show status" from the command line to find the free space on the /common partition. Using some simple math you can figure out how many logs you can save on the common partition. Make sure too that you leave some extra space on there for other things (meaning don't exhaust your free space).
