bradd@gssc.gss.com (Brad Davis) (05/16/91)
I have a problem with a SCSI tape drive that probably doesn't have much to do with SCSI per se, but since there seems to be alot of talk here involving tape drives, I'm assuming there are knowledgable tape users here in the audience. One quick aside that I should ask before launching into my tale of woe and probably losing some of you: What is everybody using to control their SCSI tape drives? I'm using SYTOS Version 3.03 AD, which is a of couple years old. Should I consider an upgrade, or is there a better alternative out there? What I would really like is to make my tape drive appear as drive E: or whatever and be able to use it as a big, sequential access floppy drive. Any pointers to SCSI tape-capable packages would be very welcome. Thanks! Now, on to the main problem, which may or may not be related to SYTOS. Since quite new to the tape drive world, I'll proceed on the assumption that I've screwed something up. Anything you can confirm, deny or suggest would be greatly appreciated. Some particulars: Archive 2150S Viper (150Mb embedded SCSI 1/4" tape drive) (internal) Adaptec 1522B (I think it's a B; it's certainly brand new) entirely factory default settings Tape: Dysan 612 (Length: 600 ft / Hci: 550 / Reorder: #815099 Certified 12500 ftpi / 60" BOT) 386-based AT clone 80 Mb MFM hard disk SYTOS version 3.03 AD I've been backing up my hard disk (life insurance, as they say) for a couple of months now and this seems to be working just fine. Each backup verifies correctly, and I have also done a test restore to make sure there were no surprises lurking in that hopefully little-used function. So I am reasonably confident that the installation and configuration is correct. Lately, I've started to use the tape drive to store file (as opposed to drive) backups. My intention is to spool unused subdirectory trees off to tape when not in use and then restore them when I need those trees again. I have only 80Mb of hard disk storage, so creating a larger "virtual hard disk" on tape is quite attractive. Since most of the packages I have been spooling off have been in the 10 to 30 megabyte range, I have been using SYTOS's "Append" option to store several backup "Sessions" onto a single tape. I verified each backup, and assumed that my data was safely record on tape. Wrong - I just found out last night that something has gone wrong. I tried to append a third backup to a tape that already had two backups on it. SYTOS went all the way through the tape, and never found whatever it uses as and end-of-recording mark. Since the first backup was 29 megs and the second backup only 19 megs, I knew I should have plenty of tape left. Fearing the worst, I went back to restore the two backups already on that tape. The last two megabytes of the first backup, and all of the second backup, are lost, or at least SYTOS can't find them anymore. When SYTOS attemts to restore or generate a directory listing of the tape, each file up until that fateful 27 meg spot is correct. Beyond that point, the drive continues to read but SYTOS no longer recognizes what is coming in as files. SYTOS does not see the end-of-session mark and just keeps seeking along until it reaches the end of the tape. I can recreate most of the lost data, but I can't really use the tape drive in any serious way until I understand what happened, how to prevent it, and hence can trust it again. I can think of several things that could have gone wrong: 1. During the writing of the first or second backup sessions, a file header or terminator got omittited or overwritten. I think I can disprove this theory: I verified both backups when I wrote them. I might not have noticed that only 27Mb of the first backup was there to verify, but I would certainly have noticed when no second backup session was found to verify. I also have another tape which has three sessions on it, and all three of those sessions are readable. 2. Something must have happened to the tape between the time I verified the second session and when I attempted the third. It seems unlikely that this damage was caused by a newly bad piece of tape: The tape is only four or six weeks old, and it has only been days since I recorded the first and second sessions. (I did retensioned the tape before recording on it the first time. I've heard this is considered to be a good precaution with many kinds of tape, so I assumed it was a good idea with these data cartridges). 3. I just realized what may very well have happened - I remember leaving a tape (quite possibly this bad one) loaded in the drive over night. This means that the tape was in contact with the head during system powerup, and who knows, maybe some voltage gets to the write head during those first few hundred milliseconds? I knew that leaving the tape in during a power cycle was "a bad thing"; maybe I just learned the hard way that it is "a very, very, VERY bad thing". Obviously, I'm not going to do this again, but does the fact that I did such a stupid thing explain this problem? The tape is always rewound to the beginning before leaving SYTOS, so the place the head could have trashed was at the very front of the tape. As I understand it, the tape has several tracks which alternate in direction. I have noted by the sound coming from the drive that each track holds about 9Mb worth of drive backup. 27Mb is indeed a multiple of 9Mb, but wouldn't the 27Mb mark be at the very end of the tape rather than the very beginning? Is it believable that it takes 36Mb worth of tape to record 300 files that total 27Mb in size? I seem to have talked myself into believing that my problem was caused by a one-time act of stupidity/carelessness on my part. Do you believe it? A related concern is the apparent fragility of the filesystem that SYTOS uses. If a single bad spot on a tape can result in losing most of the data on the whole tape, it seems I'm far more vulnerable to murphy's law than I should be. Is there a SCSI tape control package that has better error recovery? Something that writes tar-compatible tapes, perhaps? Thanks for any advice you can offer. Please email me (bradd@gssc) or post as you prefer - I will summarize to the net if anybody asks. Random drivel from the keyboard of: +--+ Brad Davis, GSS Inc, Beaverton OR _________ -_--_ ________________|80|__ bradd@gssc (503) 671-8431 -- -- =o==o= -- -- -- -- +__+ Disclaimer: The boss disavows ----------------------------------||--- all knowledge of my actions. Whfg fnl AB gb 65! ||