Copyright : Sybase,Inc.

Background

Adaptive Server devices usually are raw devices or file system devices. Solaris users have a third option, tmpfs, for tempdb.

tmpfs -- the temporary file system -- caches writes only for a session. Files are not preserved across operating system reboots.
Note:

Other UNIX platforms may allow you to create a temporary file system device. See your operating system System Administrator.

Should you use tmpfs?

To determine whether tmpfs would benefit your system, perform benchmarks comparing the memory assigned to tmpfs versus the memory assigned to the data cache.

Usually, it is more effective to give extra memory to the server for use as general data cache rather than creating a tmpfs device for tempdb. If tempdb is used heavily, then it will use a fair share of the data cache. If tempdb is not used often, then the server can use the memory assigned to data cache for non-tempdb data processing, but if the memory is assigned for tempfs it is wasted.

For more details...

http://www.sybase.com/detail?id=20448