Communicator e3000 MPE/iX Release 6.0 Express 1 (C.60.01) (30216-90286)

28 Chapter3
Technical Articles
Announcing DLT4000/DLT7000 Differential Tape Support on MPE/IX
Physical connection of these devices is accomplished via “Fast/Wide/Differential SCSI”
Cables such as C2911A, C2924A, C2925A etc.
NOTE While DLT Libraries are available for purchase, support for these devices is
very limited on HP3000 S900 systems. There are currently no plans for
supporting the DLT Libraries for “normal” MPE/iX operations such as BOOT,
FCOPY or STORE. DLT Libraries are supported only when used in
conjunction with a third party software package, Legato’s “NetWorker.”
Inquiries about DLT Library support should be made directly to Legato.
Product Overview
The performance difference between the DLT4000 and DLT7000 Differential drives is due
to data transfer characteristics. Specifically the DLT7000 is a “differential-wide” device,
transferring two bytes at a time during the data phase. The DLT4000 (C3690A), though it
is connected via a “differential-wide” cable, is actually a “differential-narrow” device,
transferring only one byte at a time. From a native (non-data compression) perspective,
the DLT4000 is capable of transferring data to tape at up to 2 Mb/Sec while the DLT7000
is capable of transferring data to tape at up to 4 Mb/Sec. When making use of the
compression feature (Digital Lempel-Ziv, DLZ) the amount of data sent to the device can be
significantly greater than the device’s ability to write to tape, depending on the
compressibility of data. However, there is an upper limit on the amount of data that the
device can accept and the SCSI bus can transfer. This puts an upper limit on the number of
devices that can be driven at peak I/O rates on a Bus. This upper limit is the “Maximum
Number of Devices Per Bus.” Of course, these figures are approximate and are reached
only on systems with sufficient available CPU resources AND Disk I/O bandwidth.
Both the DLT4000 and DLT7000 drives accept the new CompacTape IV cartridge. When
this cartridge is used, the amount of data you can store on a tape can be up to 20.0 GB
native, or an expected 40.0 GB of data using the compression mode for the DLT4000. The
DLT7000 will hold 35.0 GB native, or 70.0 GB when employing data compression. The
actual amount of data stored in compression mode is dependent on the nature of the data
being stored. That is, text files tend to be highly compressible while code files are not. Both
devices can also use the CompacTape III cartridge. The amount of data you can store on
this tape cartridge can be 10.0 GB native capacity or 20.0 GB compressed.
Product Standard,
Non-compressed
Capacity with
DLT IV
Average
Maximum Data
Transfer Rate
to Tape
Average
Maximum Data
Transfer Rate on
SCSI Bus
Maximum
of Devices
per Bus
DLT4000 (SE-SCSI) 20Gbtye ~2Mbyte/sec
~4Mbyte/sec 1
DLT4000 (FW-SCSI) 20Gbtye ~2Mybte/sec ~4Mybte/sec
2
DLT7000 (FW-SCSI)
35Gbtye ~4Mbyte/sec
~9Mybte/sec 1