djjames@althea.UUCP (Daniel James) (04/14/90)
>Article 6158 of 6185, Sat 12:14. >Subject: Re: Kronos tape drive(r) >From: crash@ckctpa.UUCP (Frank J. Edwards) >Path: ncr-sd!sdd.hp.com!elroy.jpl.nasa.gov!usc!samsung!uunet!pdn!palan!ckctpa >Larry: the CLtd docs imply that QuarterBack can be used with a regular >SCSI tape drive; just configure the tape drive as a harddisk. Since >QB talks directly to the .device it will access the tape in a sequential >manner (is there any other way?)... Any opinions? comments? I tried getting QuarterBack to talk to a SCSI tape drive connected to a GVP controller by making a MountList entry for TAPE: setting it up as 1 head, some large number of cylinders, 1 block/track and using scsidev.device. When told to backup to device TAPE: the drive tweaked the tape once and QB choked. No combination of values would work. What I did do was to make a tapedisk.device that reacted to trackdisk commands and talked to scsidev.device using scsi direct commands. Ultimately, it worked. I've been able to backup and restore from a Wangtek SCSI drive using QB without a hitch. One thing that I noticed about QB 2.3 was that it writes 1 output cylinder at a time and it computes the size of this cylinder by multiplying #heads * blocks/track * 512. Unfortunetly is uses the MULU instruction to do this resulting in a maximum write size of 65536 bytes. This gets reflected back to the MountList entry where I specified 1 head and 127 block/track. This also means that my tapedisk.device must buffer a large number of writes and output them all at on shot to get acceptable tape streaming performance. Reads are handled the same way, I read a large amount of data then parcel it out as QB requests it. I also handle seeks to arbitrary blocks needed when restoring individual files. Now the bad news. What I've done works just dandy on my system. I've used it and tested it and have complete confidence in it (I've reformatted both hard drives and restored them at least twice) but it has problems on another system using different controllers and drives. The Supra controller/drive combo crashes with GURUs when it doesn't lock up the machine. A different controller/drive combo on the same machine worked once out of a dozen times the other times apparently the SCSI bus hung. In my opinion, the fault lies with the other scsidirect implementations but I can't prove this. In any event, what I have is crude, lacks proper error handling/recovery and as such can't be released to the public. I didn't mean to tantalize and retract a goodie more to let you know that it IS possible to get QB working with at least 1 tape unit and perhaps the right people will make it work with every combo of controller/drive. I don't care to carry the effort any farther...what I have works just fine for me. Djj -- ------------------------------ Nothing fancy...djjames@althea