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Path: euryale.cc.adfa.oz.au!newshost.carno.net.au!harbinger.cc.monash.edu.au!munnari.OZ.AU!news.ecn.uoknor.edu!feed1.news.erols.com!news.maxwell.syr.edu!news.pbi.net!nntp.mainstreet.net!bug.rahul.net!rahul.net!a2i!samba.rahul.net!rahul.net!a2i!fmc.a2i!fmc From: Frank McConnell <fmc@rahul.net> Newsgroups: comp.unix.bsd.freebsd.misc Subject: Re: Finding Reliable DAT Drives Date: 28 Apr 1997 18:02:33 GMT Organization: File under Psychedelia Lines: 47 Message-ID: <5k2onp$q35@samba.rahul.net> References: <kientzleE8v0Ly.5zp@netcom.com> <5jv53r$7nc@uriah.heep.sax.de> NNTP-Posting-Host: waltz.rahul.net NNTP-Posting-User: fmc Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:39905 J Wunsch <joerg_wunsch@uriah.heep.sax.de> wrote: >kientzle@netcom.com wrote: >> Can anyone comment on DAT reliability? Is 2 out of 3 failed backups >> something I'm likely to see with a new drive? > >Did you use your cassettes more than 10 times already? That's the >limit. The throw-away-society hits... Tapes have been throwaways for as long as I can remember. They stretch, they wear, they fail in all manner of interesting ways. Some you can prevent or defer with proper cleaning of drives (and, in an earlier era, tapes). Some you can't. Some can only be deferred so long. You have to figure that the tapes will wear out after a while and you will have to replace them when they do, or better shortly before they do (and you find out about it by way of a backup that won't restore). I'd like to get a good handle on how to figure that out based on how I am using the tape. Where does one go to find information on DDS DAT life expectancy? I've seen several numbers like this regarding DDS tapes: 10 uses, 25 uses, 50 uses. Sometimes "uses" is replaced by "insertions" or "passes", which are of course different. For example, from http://www2.freebsd.org/handbook/handbook129.html: "Tapes should be retired from use after 2,000 passes or 100 full backups." As I read it that is describing 4mm DDS tapes and I am having difficulty reconciling Joerg's statement and this statement (not that I take either one as gospel -- sorry, Joerg -- or assume they both came from the same person). For that matter, assuming that dump/tar/cpio et al treat the tape as a serial medium and aren't zipping back and forth on it, I am having difficulty figuring out what the two numbers in that statement have to do with each other. ... So what am I doing now? Well, I don't buy used tapes for backups, and I stick to 60m and 90m DDS MRS media (120ms are expensive and I don't need that much for a full backup as yet -- also I expect the tape may be thinner and so more susceptible to stretching and breaking, just like 3600-foot nine-tracks were). I am assuming that I can get 50 backups out of a new tape, where each backup is one insertion and two passes (a dump and a restore -ivf to read the directory back), but haven't got there yet nor have I seen indications of failure to lead me to believe that I should lower my expectations. And I go through a cycle of tapes for each system. -Frank McConnell