friedl@mtndew.UUCP (Steve Friedl) (03/15/90)
Petri Ojala writes: > > Our intention is to replace the two small HD's in the > 3b2/600 (which are connected via ESDI--SCSI converter) > with a 3rd party SCSI disc. > > Is there anything special in doing such a replace? > Any extra drivers or configuration required ? > Anything else we should know ? This is easy or hard, depending on how adventurous and lucky you are. Mine is a long posting, so if you are not interested in 3B2 SCSI, hit 'n' now. SCSI is supposed to be standard across the board, but those who know about this kind thing (I'm not one of them) tend to snicker a lot: it's kind of like "standard RS-232". The 3B2 supports single-ended SCSI on the standard host adaptor, and by and large it will work as you expect. "By and large", however, has a large gotcha. Keep in mind that I am by no means a SCSI wizard or am even really comfortable with it. I've just been down this road a couple of times, plus a few [expensive] detours. A fellow at AT&T with whom I have had extensive conversations on this subject tells me that AT&T has never seen a SCSI drive or controller that has not had bugs. This doesn't mean the easy stuff like read or write, but it usually involves subtle error conditions under very heavy loads and all that. While AT&T certainly has a vested interest in selling their own drives, I believe my friend when he tells me this. AT&T has available what I understand is a *very* extensive test suite for SCSI, and their own internal tests are probably even better. The smaller 3B2 machines use an Emulex SCSI-to-ESDI bridge controller, and it can talk to four ESDI drives at a time; this controller is in the machine Petri is describing. The newer/larger machines use drives with embedded SCSI controllers, with no bridge adaptor anywhere. When a machine is booted, some part of the machine asks the drive "who are you?" -- the SCSI Inquiry -- and the drive responds with its SCSI ID. This indexes into the extended equipped device table, where this ID says what kind of device it is, how many logical units are supported, which driver is to be used, and the like. If you boot the machine with an unknown SCSI device, it will tell you this and mention the ID it does not understand. These IDs are composed of the vendor name and a product name, and they are easy-to-read ASCII (ie, "EMULEX MD21/S2 ESDI"). Adding a new entry to the extended equipped device table is easy. There is a SCSI version of the "edittbl" command, probably found under /etc/scsi.d or /usr/lib/scsi (your location may vary) and there are lots of other things here. You answer a bunch of straightforward prompts and you have built the table. The problem is that you never know whether you did it right. While it is easy to get the disk/tape/optical/etc. distinction right, there are several flavors of each of the disk drivers. Each of these drivers has a parameter file with information needed by the formatting program, and it is impossible to figure out without serious documentation from AT&T. For instance, this is the file used for a particular HP drive: #-------------------------- cut here ---------------------------- DISK MODE SENSE : 1A0003001C00 MODE SENSE : 1A0004001800 FORMAT : 00000000 040000000100 FORMAT WITH DEFECTS : 00000000 041D00000100 00800000 READ CAPACITY : 25000000000000000000 DISK INFO : FFFFFFFF 0000000C 0000 0000 0000 0000 VERIFY : 2F000000000000000000 READ DEFECT DATA : 37001D00000000000000 #-------------------------- cut here ---------------------------- Some of these are obvious (# of cylinders, etc.) but others are a total mystery to me. Those familiar with SCSI might be able to figure this out, but I was not that experienced with it. While you can probably get away with somebody else's parameter file, I don't think you can count on getting it all right. We bought a surplus HP drive whose ID was almost identical to an official AT&T-supported one, so we are pretty sure that the formatting is OK. We have not had a lick of trouble with the drive since we installed a couple of months ago. It is also possible to really get it wrong. A net.friend of mine (hi Bob!) and I never did get a Maxtor SCSI drive (don't recall the model) working, and it could have been anything. Furthermore, SCSI is supposed to be the same on the 3B2 as on the 3B15 and 3B4000, and we have found this to be largely the case. We found some interesting problems with AT&T's standard DCM/4E, the Emulex ESDI bridge adaptor, that took some (ahem) cleverness to figure out. Those interested in expanding their 3B15s are welcome to write for details. Your best bet is to dig up your local list of supported drives and buy one of them. You can get it cheaper than AT&T's and if you can do your own install you'll have a really nice setup. Note that as of a month or two ago, AT&T would not support *any* third-party ESDI or SCSI drives, even if the models were identical. I have heard rumors of data techs being fooled on this matter, however. Sorry for such ramblings, hope this is helpful to somebody. Questions/responses are welcome. Steve -- Stephen J. Friedl, KA8CMY / Software Consultant / Tustin, CA / 3B2-kind-of-guy +1 714 544 6561 voice / friedl@vsi.com / {uunet,attmail}!mtndew!friedl "How could anybody look at Miss April and *not* believe in a God?" - me