tomk@attctc.dallas.tx.us (Tom Karches) (02/04/90)
We currently have an Hewlett Packard 35450A Digital Audio Tape (DAT) tape drive on evaluation, which is connected to a 4/110 with a external disk box. This drive is somewhat similar to the Exabyte drive except it uses 4mm DAT tapes instead of the 8mm video tapes, and the capacity is lower at 1.3 vs. 2.2 gigabytes. The documentation specifies that it is possible to search the tape at 200 times normal speed with this drive, which it does not seem to be doing with the TAR command. We are using the device driver /dev/rst1 with the drive, which is the driver for the standard 1/4 inch cartridge tape. I believe that the 1/4 driver does not support the command in the DAT drive hardware that initiates the high speed search (SPACE command). This brings me to the question : What would be involved with either adding this capability to TAR or developing an alternate driver that could take advantage of the high speed search capability? I would be open to modifying existing code to achieve this; would GNU TAR be a good starting point? It seems to me that this high speed search capability (less than 20 seconds to find a file on a 1.3 gigabyte tape) appears to be a major advantage over Exabyte based drives. I have also heard that the DAT drives are more reliable; any comments? Thanks, Tom Karches Texas Instruments, Dallas 214/480-4468
henry@zoo.toronto.edu (02/09/90)
>We currently have an Hewlett Packard 35450A Digital Audio Tape (DAT) tape >... documentation specifies that it is possible to search the tape at 200 >times normal speed with this drive, which it does not seem to be doing >with the TAR command... If I am not mistaken -- I'm not very familiar with those things -- the capability in question is a high-speed *seek* not a high-speed *search*. That is, you can use the high speed only if you know exactly where you want to go. Unfortunately, tar doesn't; it really does have to read the stuff going past to decide whether it's reached what you're after. Henry Spencer at U of Toronto Zoology uunet!attcan!utzoo!henry henry@zoo.toronto.edu