CLINTON SCHWARTZ ([log in to unmask]) wrote:
: Does anyone have any numbers comparing the read and write rates of DAT tape
: drives versus the Reel to Reel tape technology.  We have reel to reel tapes
: and would like to see if upgrading to DAT's would be worth it.  Thanks!
:
We need to be a bit more specific about what rates and tape drives are
wanted.  RE HP DDS drives (note DDS is a subset of DAT) the 60 Meter and
90 M drives have a native transfer rate of 183KBytes/sec.  The new 120 M
drives have a 510KB/sec rate.  The 7980's rate is 781KB/sec.
 
But for Backups using HP TurboStore (or other products) the capacity of the
tape media, mounting and rewind times, channel capacity and usage, and
compressibility of the data, and who does the compressing (hardware or
software) must be considered.
 
For an actual datapoint, I have a 3000/947 which backs up about 17 million
sectors (4.3 Gbytes) and it takes about 3.5 hours with software compression
to a 90 M DDS.  It uses about 2.4 hours to a 120 DDS with hardware
compression.  That is 1.25 GB/Hour and 1.83 GB/hr respectively.  This
may be somewhat limited by the tape and discs being on the same SE SCSI
interface.  Note that this is a low compression ratio as if I add only a few
more files to the backup the 90 M DDS goes to two tapes.
 
For one reel STOREs the 7980XC is faster, but for the storage and convenience
of one reel Full Backups, DDS with compression is King.
 
James Overman  HP Support Technology Center