dan@msdc.UUCP (09/20/83)
This is just a word of warning for all of you out there that have notions of dual-porting the RA series disks. After much hassle with our local DEC office we finally got our hands on the MSCP documentation so we could fix the Unix driver to support RAs shared between two processors (not file systems, mind you, just drives). After wading through an incredibly opaque and obfuscatory swamp of verbiage, we questioned our marketing friends' statements that the drives were dynamically dual ported. After allowing for the fact we were somewhat "uninitiated" to the marvels of DSA (and after threatening bodily harm) we were allowed to talk with an engineer in Colorado who knew the real story. Without giving away any of the marvelous secrets we agreed not to disclose, it turns out that the RA drives are indeed dynamically sharable. However, THE **@@#@* UDA50 DOES NOT AND WILL NOT SUPPORT dynamic dual access to drives. The only way it can be done requires about 800ms to switch a drive. Unless, of course, you shell out another $150K for a redundant HSC50 configuration--THEN AND ONLY THEN CAN YOU ACTUALLY DYNAMICALLY SHARE DRIVES BETWEEN PROCESSORS. (In all fairness, the static sharing works just fine--if a machine dies, you can indeed switch the drive to the other machine.) If you are interested in how we could be so badly misled, just whip out your systems&options guide and look at the descriptions for the RM05 and RP07 (real dual access drives) and for the RA disks. See if you can tell that the UDA50 doesn't support dynamic dual access! We sure couldn't. And neither could the local sales office. (And anyone who says "That's what you get for listening to a salesman" will meet with an exceedingly unpleasant demise.) Dan Forsyth (...sb1!msdc!dan, ...allegra!gatech!msdc!dan) Medical Systems Development Corporation