Date: Tue, 24 Dec 1996 05:47:39 +0100 (MET) From: grog@lemis.de To: aat81@dial.pipex.com (Simon Reading) Cc: freebsd-hardware@FreeBSD.org (FreeBSD hardware Users) Subject: Re: DAT reliability Message-ID: <199612240447.FAA02885@freebie.lemis.de> In-Reply-To: <3.0.32.19961223225320.006855dc@pop.dial.pipex.com> from Simon Reading at "Dec 23, 96 10:56:02 pm"
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Simon Reading writes: > Thanks to those of you who are participating in this thread. > > In my original post: >> I had an HP C1533A DDS-2 drive which worked fine, but which I exchanged > for a sony SDT-7000 DDS-2 because of the reliability warnings given in the > FreeBSD Handbook. Unfortunately my sony drive is broken - I/O errors on > read, can't format tapes using the Adaptec EZ-SCSI utility etc. > > In this email, I explain what my setup was for both the HP and Sony DDS > drives. I RETURNED THE SONY TODAY because it was the last day I could do > so and get my money back. I have not purchased a replacement yet as my > choice is dependent on the outcome of this thread :-) > > I think there are a number of issues: >> How reliable is DDS/DDS-2 (DAT) technology? >> Is any one brand of DDS drive better or worse than another? > (or 'Do the HP drives warrant their Freebsd warnings?') >> Can anything be done to extend DDS drive life? >> Is there a common failure mode for DDS? > >> From mail that I have received I am beginning to believe that the DDS > mechanism, or more precisely the head, wears out and break down. Sure. That's valid for all tape drives. The real question is, how quickly? The jury's still out on that one. > I don't know if HP drives are better or worse than any others. That said, > I have been put off the Sony SDT-7000 as 1) my problems with the unit > supplied to me, 2) on the basis of replies, few seem to be in circulation > (are sony users at bleeding edge?) and 3) I can't see how the high > rotational speed of the SDT 7000 can do anything but degrade reliability > (cf HP). It can also improve performance. > Dave (dtsao@puc.edu) wrote: >> If you can purchase the Sony 7000 for $40 more than the Sony 5000 DAT, and >> the *only* difference is that the 7000's RPM is 8503 while the 5000's is >> 4000, would you buy the 7000? Is it as reliable and safe when running at >> that speed? My HDD doesn't even come close! > > On the general subject of DAT reliability, phr@netcom.com (Paul Rubin) writes: >> I have a C1533a now a little over 1 year old. I've had no problems >> with it but my usage has been pretty light. Any DAT drive will >> wear out after a year or so of heavy usage. DAT is built around >> consumer audio media designed for low cost, and the mechanisms >> are too fiddly to be really durable. Same goes for 8mm only more so. >> If you want reliable backup and can pay for it, get DLT. Otherwise >> DAT is the best bet. I don't know if I agree with that. Sure, it's built on the original DAT technology, but that doesn't make it a consumer grade article. Note that the estimated MTBF of the C1533A is 4 times that of the 35480A. They're obviously doing something there. > Unfortunately I can't afford DLT, so DAT it is . . > > Greg Lehey <grog@lemis.de> enquired of my setup: >>> He really wasn't that clear about what didn't work for him, >>> and it may be something silly like using audio grade tapes, >>> which can't be written to (unless some DIP switch is set to >>> a non-default position, which might have been the case for >>> his HP drive). >> >> Yes, that's correct. It was one of the problems I was thinking of, >> too. Let's wait for his reply. > > Here are my setup details: > > Hardware setup 1: > Adaptec 2940 (non ultra) > HP C1533A DDS-2 (internal, connected via adaptec internal cable). > The DAT drive is the only device on the SCSI chain. > > Tapes which I used successfully on the C1533A: >> HP DDS 60 metre. >> Sony 90 metre computer grade DDS-2. To the best of my knowledge, there ain't no such beast. The 90 metre tapes are all DDS-1. You need the much more expensive 120 metre tapes to get DDS-2. But at least you weren't using audio grade tapes. > Dip switch settings: >> Compression enabled at power on, with host control. >> Media recognition active. >> Caution on hard error. >> Parity on. >> Data phase disc. >> Truncate request sense off. >> Variable block size mode. >> SCSI id 3 > > Hardware setup 2: > > Unsuccesful Setup with sony SDT-7000 (connection as above). >> SCSI id same as for HP DAT >> DC disable (tried both ON and OFF) - what is this? Data compression. Unless you're exchanging data with somebody who doesn't have data compression, leave it on. >> SCSI parity on. (both settings tried) >> Termination on. (both settings tried) > > The Sony package which I received had evidence that it had been opened (a > faulty return?). >From what you say below, it's beginning to sound like it. > Problems with the sony were: > - Excessive lacing and unlacing of the tape on boot up (it really seemed to > be making a meal of it). Ah, yes, this sounds familiar. That's typically the way my 35480As died. Was this a brand new tape? I've had cases where a tape written on a bad drive can confuse a good drive. > - Inability to format Sony DDS-2 tape using the Adaptec EZ-SCSI utility: > (read errors, tape removed from drive during format etc). I don't understand this. DDS tapes don't need formatting. What did the documentation say on the subject? EZ-SCSI is a DOS utility, and you don't need it. Or are you running this under DOS? EZ-SCSI supports all tape drives, some of which need formatting, and I wouldn't put it past the program to run into trouble if you try to format a drive that doesn't support formatting. > - device I/O errors when trying to read a tar archive created by the HP and > another DDS drive. It's always better to give the error messages rather than just a statement like this. What were the errors? For example, my newly repaired Exabyte still shows the same problems :-( Dec 23 12:02:03 freebie /kernel: st1(aha0:5:0): MEDIUM ERROR info:10000 csi:0,0,0,13 asc:3,2 Excessive write errors Dec 23 12:02:04 freebie last message repeated 2 times Dec 23 12:02:05 freebie /kernel: st1(aha0:5:0): MEDIUM ERROR info:10000 csi:0,0,0,13 asc:3,2 Excessive write errors Dec 23 12:02:05 freebie /kernel: st1(aha0:5:0): MEDIUM ERROR info:10000 csi:0,0,0,13 asc:3,2 Excessive write errors Dec 23 12:02:05 freebie /kernel: st1(aha0:5:0): MEDIUM ERROR info:10000 csi:0,0,0,13 asc:3,2 Excessive write errors Dec 23 12:02:06 freebie /kernel: st1(aha0:5:0): MEDIUM ERROR info:10000 csi:0,0,0,13 asc:3,2 Excessive write errors Looking at the first item on your list, however, I think I'd agree that you do (did) have a defective drive. You will probably not have any problems with a replacement. Greg
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