Michael,
       Is your rate 7GB/hr for a single stream realized during an off-line
backup (Oracle is down), or while Oracle is up and in use in backup mode?
      Tuning backup performance in an on-line mode complicates quite a bit.
Our system is 24 by 7, is made up of multiple SP2 towers and RS6000 R30
systems, and we're expecting to exceed a terrabyte per database in a few months.
       The issue of interleaving or multiplexing backup sessions to a single
tape is an issue I've also raised with IBM.  The usual response is to suggest
buying more tape drives, one per backup session.  But, as you said, the 3590
tape drive is NOT cheap .  Given the the 3590 is rated to accept data at a rate
of over 10MB/second, and the disk drives and systems can only sustain a single
backup session rate of 3MB/second (absolute peak), we either need to make
better use of the 3590's or use a more economical, lower speed tape drive with
ADSM.  Other vendor's backup products support interleaving/multiplexing, why
not ADSM?   IBM recently announced selling another product that DOES profess to
support interleaving, but it doesn't seem to be integrated with ADSM or SAP.
      One help for this problem of performance may be use of Oracle's obackup
utilities with ADSM, when it becomes available (I believe it's expected by
September sometime).  Oracle itself can interleave backup sessions of its
database components BEFORE feeding it to ADSM for transfer to tape.   My
current problem is getting SAP to respond to my questions about if/when using
these features of obackup with ADSM  will be supported by their SAPDBA tool set.
          John Howard