merrick@magnus.ircc.ohio-state.edu (Tom Merrick) (01/01/91)
I found a couple of unexplained things while using backup at the 3002 level and 1/4" low density cartridges (rmt0.4 and rmt0.5). First, I wrote a tape label using dd, forward spaced over it, then did a backup to the cartridge. I got a write error stating that I had defective media. Second, I did several backups to the same tape cartridge (w/o a tape label). Everything finished correctly, so I did a tcopy on the tape and found out that my 60 MB cartridge had almost 112 MB on it! Is backup ignoring the hardware and always writing high density? This would explain both problems above. Tom Merrick Ohio State University
torre@msa3b.UUCP (Patrick Torre) (01/01/91)
merrick@magnus.ircc.ohio-state.edu (Tom Merrick) writes: >Second, I did several backups to the same tape cartridge (w/o a tape label). >Everything finished correctly, so I did a tcopy on the tape and found out that >my 60 MB cartridge had almost 112 MB on it! >Is backup ignoring the hardware and always writing high density? This would >explain both problems above. >Tom Merrick >Ohio State University I was having the same trouble, still am actually, thing is , I found that low density is 120meg and high is 150 meg. I came to this conclusion looking through the doc from the IBM AIX v3 System Administators class. you need dc6150 tapes to get 150 meg on a tape, and you'll pay extra $$ for the extra 30 meg. -- Patrick Torre @ Dun and Bradstreet Software, Inc (404) 239-2061 {emory,gatech}!nanovx!msa3b!torre
bob@cadlab.sublink.ORG (Lanfranco Albani) (01/02/91)
>Second, I did several backups to the same tape cartridge (w/o a tape >label). Everything finished correctly, so I did a tcopy on the tape >and found out that my 60 MB cartridge had almost 112 MB on it! > >Is backup ignoring the hardware and always writing high density? This >would explain both problems above. I believe there is something more to it... the AIX filesystem structure is tricky, but what I _think_ is happening is that full 8-Kbytes blocks are being used, thus with an average of 4 Kbytes wasted per file; df is reporting on a full-block basis; and tape backup is NOT copying the extra per-file 'slack', only the "meat" of each file (I'm not sure what both df and tape backup are doing with holey files, but I would guess them to be more in-sync in this respect). I had a filesystem occupying 190 megabytes, and its backup fitted inside a single DC6150 150-Mbytes tape; and I don't even know if that tape was actually full... no problems re-reading it, anyway! Well, at least this is saving us tapes! -- Lanfranco Albani - CAD.LAB s.p.a., v. Stalingrado 45, Bologna, Italia Email: (work:) bob@cadlab.sublink.org, (home:) bob@allan.sublink.org Phone: (work:) ++39 (51) 371099, (home:) ++39 (51) 727372; Fax: ++39 (51) 366964 (work only), Fidonet: 2:332/401.4 (home only).
lerman@stpstn.UUCP (Ken Lerman) (01/05/91)
In article <1990Dec31.183601.17768@magnus.ircc.ohio-state.edu> merrick@magnus.ircc.ohio-state.edu (Tom Merrick) writes:
.I found a couple of unexplained things while using backup at the 3002 level
.and 1/4" low density cartridges (rmt0.4 and rmt0.5).
.
.First, I wrote a tape label using dd, forward spaced over it, then did a
.backup to the cartridge. I got a write error stating that I had defective
.media.
.
.Second, I did several backups to the same tape cartridge (w/o a tape label).
.Everything finished correctly, so I did a tcopy on the tape and found out that
.my 60 MB cartridge had almost 112 MB on it!
.
.Is backup ignoring the hardware and always writing high density? This would
.explain both problems above.
.
.Tom Merrick
.Ohio State University
My understanding of these devices is that while the high capacity
devices can read both high and low capacity tapes, they can only write
high capacity tapes. The capacity is determined by the number of
tracks which the drive writes. Since the high capacity drives have a
narrower head, there is no way for them to write the wide tracks
required to write in low capacity mode.
Ken