Re: SCSI interfaces; we have seen DLT7000 drives with both
     single-ended and FWD.

     Paul Meszaros
     ORBiT Software
     [log in to unmask]


______________________________ Reply Separator _________________________________
Subject: Re: DLT4000
Author:  [log in to unmask] at internet
Date:    8/19/97 4:52 PM


On Tue, 19 Aug 1997 14:47:17 -0400,
Juan Pineiro <[log in to unmask]> asked:

|Anyone out there using DLT4000 on a HP3000 box?

There is a relatively small but growing group using DLT drives on the 3000.

|Anybody know if Roadrunner supports DLT4000?

RoadRunner supports DLT4000 drives on MPE/iX 5.0 and 5.5 with the
appropriate patches available from HP.

|How much data are you squeezing into a tape, How many gig/hour?

The DLT4000 drive corresponding CompactIV media are rated at 20GB native
capacity and 40GB compressed capacity.  The compression ratio of 2:1 is
very dependant on the data being recorded on the drive.  MPE production
systems often see better compression ratios than that; 4:1 is not uncommon
and I have personally seen a real-world production system get slightly
better than 10:1 compression.  Although I am not familiar with all the
details of the compression algorithm used in the DLT drives, I understand
that it is a variant of the LZ (Lempel-Ziv) technique.  RoadRunner's high
compression option is also an LZ-based algorithm and might be used to
estimate how compressable your data is by enabling the appropriate
COMPRESS and DISPLAY options.

How fast data is sent to the drive is mostly dependant on the CPU and the
I/O bandwidth for the disc and tape drives.  In some unusual circumstances
other factors such as system memory impact performance.  On systems with
adequate resources, DLT drives outperform all other tape devices I have
used by a clear margin.

|Can I piggy back 4 DLT4000 drives off of on one FWD/SCSI channel and
|run parallel backups without a performance loss?

Only if your CPU or disc I/O throughput is even more limited than that of
the tape drives.

|What about DLT7000? Any chance it will be supported under MPE before
|mid-98?

Officially supported?  I have no idea and probably couldn't say if I did.

Will it work?  Very possibly.  While I have not tested a DLT7000 drive yet,
I have been led to believe by a DLT hardware vendor (one of those companies
that builds tape libraries around Quantum's DLT mechanisms) that the DLT7000
should be compatible with the DLT4000 to the extent that no software changes
should be needed.  Only actually plugging one in and testing it will answer
that and I don't know of anyone who has done it yet.

BTW, the DLT4000 is available with both FWD (Fast-Wide-Differential, aka
16-bit) and SE (Single-Ended, also known as 8-bit) SCSI interfaces, however,
the DLT7000 (or so I have been told) will only be available with wide SCSI
interfaces.  [Whether that is FWD only or includes FW without D, I don't
know.  In either case, it's my understanding that all wide SCSI interfaces
available on the HP3000 are differential.]

|Thank in advance for your help on this.

You're welcome.  I hope you find this helpful.  If you have other questions
about RoadRunner and DLT working together, please don't hesitate to contact
our support group at [log in to unmask] or 512-478-0611.
--
Jeff Woods
[log in to unmask] at Unison Software
[log in to unmask]   at home  [PGP key available here via finger]

"You can discover what your enemy fears most by observing the means he uses
 to frighten you."  --  Eric Hoffer, in "The Faber Book of Aphorisms", 1964