I agree with your comments and yes if your server/client can stream data fast enough to the tape drive you may be able to out-pace a disk drive. If you can not keep up with the tape drive then you can take a serious performance hit when the tape stops, repositions and restarts. This performance hit is not as great with a virtual tape.
We also looked at the "3494 VTL or Tape Server" and saw that it is indeed a poor fit for TSM. Most TSM configurations already have a disk based stgpool front-end to the tape library so you would not gain much by adding one inside the library. Than H. Milton Johnson -----Original Message----- From: ADSM: Dist Stor Manager [mailto:[EMAIL PROTECTED] On Behalf Of Richard Sims Sent: Tuesday, November 30, 2004 9:36 AM To: [EMAIL PROTECTED] Subject: Re: size of active vs. inactive? On Nov 30, 2004, at 9:58 AM, Johnson, Milton wrote: > ...Needless to say, I disagree with the statement that TSM doesn't > appear to be a good fit for a VTL. Remember a VTL is just a library > that can mount/unmount a tape in less than one second and read/write > to the tape at disk speeds. Why wouldn't TSM work well with a library > on steroids? ... Thanks for sharing your experience with VTL in a TSM environment: it's helpful to have the perspective of experience. As we've seen in past tape vs. disk discussions, though, don't regard "disk speed" as some kind of ultimate data processing I/O attainment: high performance tape technologies streaming to sequential media can in many cases out-pace disk throughput. It is in mounting and tape positioning that tape is a poor performer relative to disk, where one can wait a minute or more before I/O can proceed. That's were VTL shines. Richard Sims