Date: Tue, 24 Dec 1996 19:03:15 +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: <199612241803.TAA00729@freebie.lemis.de> In-Reply-To: <3.0.32.19961224150632.00691884@pop.dial.pipex.com> from Simon Reading at "Dec 24, 96 03:08:04 pm"
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Simon Reading writes: > At 05:47 24/12/96 +0100, Greg Lehey <grog@lemis.de> wrote: >> Simon Reading writes: >> 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. > > Mmm. I wonder what they _are_ doing? Lots of things, I would imagine. For example, making the drums out of something more durable. Stefan said (in private mail) that Sony have a special technology for the 7000, he thinks something like an air cushion under the tape. >> 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. > > Brand new Sony 90m DDS tape. Seems to eliminate that one. >> 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. > > Quite correct. 90m tapes are DDS. On the box it said compatible with > DDS-2, which is where my typo came from. I am using 90m tapes as 1. I > don't have a need (yet) to store 4gb, 2. 120m tapes are thinner, 3. 120m > tapes cost four times as much. I'll go for (1) and (3). I haven't seen any problems with the thickness of 120m tapes. I use both in the C1533A (and in the Archive changer that I have just bought). >> - 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. > > My previous experience was using a Colorado Trakker 700 (and nobody dare > tell me that was a fast and reliable product :-). The trakker did require > formatting, about 3-6 hours of it, to be precise. My Adaptec 2940 card > comes with Adaptec Backup on the EZ-SCSI disc. When using this utility > under Windows 95, I formatted DDS tapes before initiating a backup. I > would guess that this 'formatting' action would merely write an empty > volume catalog to the tape (containing the name of the tape etc.) which > would mean something to the Adaptec Backup application itself (hence this > operation only took 90 seconds) and might include retensioning. DDS tapes don't have a volume catalogue. I suppose the Adaptec backup might use it anyway, which IMO is another reason not to use it. It really destroys interchangability. > With the HP C1533A, there were no errors when formatting (writing directory > info) to the tape. > With the Sony SDT7000, it gave errors gallore. It would be nice to know the messages, but considering it could hardly load the tape, I suspect that they wouldn't say too much. >> - 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 > > Hmm. Where did these diagnostics get output? I executed tar from the > console and was told 'device I/O error', _NOTHING_ more than that! > Unfortunately I can't try it again, since I no longer have the drive ;-) > Is there a kernel config option for specifying the level of diagnostics? They should have appeared on the console. They're output by the system to syslogd, and syslogd writes them whereever you tell it. Check /var/log/messages, whence I extracted these messages. >> 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. > > You're probably right. However, my faith in the Sony (which incidentally > was shipped without any installation instructions) has been dented. Don't be too sure that that wasn't your retailer. They frequently sell things in two forms: with tape, software, cables and lots of packing, or just the naked drive. I have had problems with Sony for the way they have to do things differently (like putting the SCSI connector in the wrong way round, so you have to twist the cable to fit), and I thought the drive itself could have more written on it, but to my recollection the drive I was given had instructions. > Michael Smith <msmith@atrad.adelaide.edu.au> wrote: >> Simon Reading stands accused of saying: >> 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. >> >> I don't understand this; you don't "format" DAT tapes. The sony >> units ignore the "erase" command because it makes no sense. > > See the reply to Greg above. > >> Are you sure you're conditioning your DATs correctly? You will find >> that a tape that's been in storage should retensioned (wind to end of >> media, rewind), and must be at room temperature for best results. >> Instructions on this sort of thing are included with most decent >> blank tapes. > > The tapes I have used were at 21C, normal pressure and humidity. > I did not retension the tape (unless this was done as part of the Adaptec > Backup 'format' action), but I had used them successfully on the HP C1533, > no problems. I will retension new tapes in future. Mike wrote this before you mentioned the load problems. I think they put the whole thing into a very different perspective. > No instructions were provided with HP or Sony DDS cartridges. I just opened a brand new HP DDS-2 cartridge (120m). On the back of the label foil there are pictures suggesting that you should tape a red cross to the cartridge and then attack it with a horseshoe, that you should wobble the read-protect tab backwards and fowards while inserting, and that you should lay a thermometer on the cartridge. Could be I'm misinterpreting this, but there is no text to go with it. In addition, they write: * Cleaning your DDC drive with HP's DDS Cleaning Cartridges is important to maintaing the performance of your drive. * Recommended cleaning frequency: (rather silly table) Another 4 points about cleaning the drive. Nothing about retensioning. One point to you. >> We've been using and recommending to our customers the Sony SDT-5200 >> (DDS2, no compression) for over a year now, with no problems at all. >> Several of these units are operating in arctic/antarctic conditions, >> and there's one in a hut in Indonesia. We receive tapes from all of >> these sites on an occasional basis and, modulo conditioning shortcuts, >> have never had any trouble reading them. > > I doubt whether my problems were to do with conditioning, I am sure that my > SDT-7000 was faulty. > > Do you have any experience of the SDT-7000? The SDT-7000 has a drum > rotational speed twice that of the SDT-5200 (as Greg noted, to enhance > performance). Running a drive at a higher speed can only make it more > susceptible to mechanical failure. I would guess that the 5200 has been > out for longer and that any bugs/problems would be more likely to be > observed/sorted out than any with the 7000. The small price difference > between the two models make me think that there has been little change in > the funamental mechanism design and that 8000rpm may be too fast to > transport the tape using the existing mechanism. I honestly don't think so. The C1533A rotates at 5400 rpm, significantly faster than the 35480A, and despite that it's more reliable. Remember that they're learning things about the drives as they build them. HP's suggested MTBF of 200,000 hours for the C1533A vs. 50,000 for the 35480A suggests that that's the case. From what I've heard, I would think that the SDT-7000 might just be the best DDS-2 drive available, and that you've just been given a dud. I wouldn't let that experience shake your confidence completely: I'd go back to the dealer and say, "OK, that device may have been a dud. Give me another, in original packing, and I'll try it again". > PS I hope Greg has more success with his exabyte drive. So do I :-) But I fear the guys who repaired it fixed the wrong problem. They assumed a drum failure, though what I've heard through other channels (the Exabyte specialist at Siemens-Nixdorf), drum failures are relatively uncommon. In case anybody out there recognizes the problem: When I start a backup, everything runs fine. By observation, the drive writes without any backing up (i.e. backtracking and re-reading or writing). After about 30 to 50 minutes, it starts backing up, and shortly after that it can't recover the data even after 20 backups, and the backup aborts. I've tried several tapes, including brand new ones, and of course I have cleaned the drive with an original Exabyte cleaning cartridge. Greg
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