VTAPE is a super product, but also consider a Flex-CUB (essentially a channel attached PC that can present itself as tape drives or slower disk volumes. You can attach a variety of lower-cost disk storage to the Flex-CUB, and mirror that, or use a variety of techniques to get that to higher-density offline storage.
The Flex-CUB boxen also do emulation of 3xxx tape drives on selected SCSI drives, which is mighty handy in a lot of cases.
