filbo@deeptht.santa-cruz.ca.us (Bela Lubkin) (05/04/91)
In <5761@media-lab.media.mit.edu.MEDIA.MIT.EDU> Masaru Sugai wrote: >This is a silly question for hardware wizards, but I would like to know how my >QIC tape drive stores data on tape. > >Today I bought a 3M DC6150, and tried full backup again but the result was >similar. Tape was wound to near the end after dumping 27MB in 440 sec. I >noticed there were changes in the motor sound, and I stopped tar 150 sec after >invocation to find out the tape was almost 'wound up'. I went through A3070 >installation guide and made a simple calculation. > > DC6150 media volume 7,440 inches (620 ft) > Data density 10,000 BPI | realistic backup time > 9.3 MB | 2 min 30 sec > Number of tracks 18 | > 167.4 MB | 45 min > >My calculation seems to be reasonable as 27MB backup amounts to one and half >r(w)ound trip. This is my last concern on A3070 which has been holding me off >100% confidence over two weeks. Any info is appreciated. Your calculations are reasonable. The QIC150 format places 18 tracks on a tape. Each track is written by winding the tape completely from one reel to the other; so a complete backup, filling an entire tape, takes 18 trips from one end of the tape to the other (9 round-trips). The figure of 9.3MB is slightly off: remember that in computer speak, "MB" means 1024*1024 bytes. The tape gets about 8.8MB per track; about 159MB for the whole tape. The drive automatically compensates for bad spots on the tape. The excess size is sufficient to allow most tapes to fit the rated amount of data (150MB). A 150MB tape that stores less than 150MB is probably physically damaged (left out in the sun?) and should be discarded. (However, depending on the drive and the software you're using to back up, it's possible for space to be wasted if the tape doesn't stream. Then the tape's fine but the software should be shot). Bela Lubkin * * // filbo@deeptht.santa-cruz.ca.us Witty quote omitted... @ * * // belal@sco.com ...ucbvax!ucscc!{deeptht!filbo,sco!belal} R Pentomino * \X/ Filbo @ Pyrzqxgl +1 408-476-4633 and XBBS +1 408-476-4945