Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!cmcl2!husc6!rice!sun-spots-request From: nielsen@saturn.ecs.umass.edu Newsgroups: comp.sys.sun Subject: Re: What is the 'real' tape length Message-ID: <8812211847.AA01513@saturn.ecs.umass.edu> Date: 3 Jan 89 13:19:35 GMT Sender: usenet@rice.edu Organization: Sun-Spots Lines: 72 Approved: Sun-Spots@rice.edu Original-Date: Wed, 21 Dec 88 13:47:02 EST X-Sun-Spots-Digest: Volume 7, Issue 84, message 3 of 14 > We have a Sun 3/260 running SunOS 4.0. The tapes that I buy for the Sun > say on them "600'", which I assume means 600 feet. However, when I use > dump, and specify a size longer than 600', it does not fail until > somewhere near 1000' (at least that is what it reports). It is tough to comment on this without seeing the entire command you used. Later in this posting is some general info on 'dump', some of this info is condensed from Sun Spots postings on Jun. 30 1988 and Aug 18 1988. We shared a similar experience with tape lengths being strange. It was *due* to our using the a density of 10,000 (YES TEN-THOUSAND), the standard blocking factor, and NOT using the 'c' (for cartidge) option. Through trial and error we found that 1100 feet was a safe value. We used the 10,000 bpi density as was given on the tape. The man on dump given on the tape. The man on dump is written primarily for reel tapes, and since they write on 9 tracks serially (as opposed to the cartridge's 9 tracks sequentially), we were confused between bits per inch and bytes per inch. {A reel tape writes a byte at a time serially} Our backups AND restores were always successful... until our tape drive died. Before we determined the drive was broken, we started investigating our dump parameters more carefully and became aware that our parameters were unusual. -> A question is: Why does density effect the tape length? It *shouldn't*, but it does. -> Another question is: Is it safe to backup using the {unusual} command: % /etc/dump "$level"usdf 1100 10000 /dev/rst8 "$filesystem" IT HAS ADVANTAGES if it is safe. It had worked reliably for over a year, takes LESS THAN HALF the time, and stores about 60 Megs of data per tape. I asked SUN about this, but they never got back to me. Most of the following info is condensed/excerpted from Sun Spots postings on Jun. 30 1988 [Dan Franklin] and Aug 18 1988 [John Gilmore]: A suggested dump command is: /etc/dump "$level"ucsbf 4800 126 /dev/rst8 "$filesystem" The "c" indicates the use of a tape cartiridge u is to update the '/etc/dumpdates' file 4800 is the tape length used for 600' tapes 126 is the blocking factor with the c the density defaults to 1000 Lowering the blocking factor decreases the amount of data stored on each tape {bad} and the time required for a dump {good}. The cartridge tape drives write 9 tracks sequentially, that is why the 4800' tape length is used (9 X tape-length X 0.95 {safety factor}). [excerpted: