Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watnot!watmath!clyde!cbatt!ucbvax!jonathan@seismo.CSS.GOV@vuwcomp.UUCP From: jonathan@seismo.CSS.GOV@vuwcomp.UUCP Newsgroups: mod.computers.vax Subject: Submission for mod-computers-vax Message-ID: <8702250915.AA05925@vuwcomp> Date: Wed, 25-Feb-87 04:15:15 EST Article-I.D.: vuwcomp.8702250915.AA05925 Posted: Wed Feb 25 04:15:15 1987 Date-Received: Fri, 27-Feb-87 23:52:10 EST Sender: daemon@ucbvax.BERKELEY.EDU Distribution: world Organization: The ARPA Internet Lines: 64 Approved: info-vax@sri-kl.arpa Path: vuwcomp!jonathan From: jonathan@vuwcomp.UUCP (Jonathan Stone) Newsgroups: mod.computers.vax Subject: Re: The WHY of a RAM disk Message-ID: <12633@vuwcomp.UUCP> Date: 25 Feb 87 09:15:14 GMT References: <8702140251.AA04388@ucbvax.Berkeley.EDU> Reply-To: jonathan@vuwcomp.UUCP (Jonathan Stone) Organization: Comp Sci, Victoria Univ, Wellington, New Zealand Lines: 53 In article <8702140251.AA04388@ucbvax.Berkeley.EDU> DHASKIN@CLARKU.BITNET writes: >> Excuse me, but I didn't realize there was anyone out there running a Vax on >> floppy disks. W H Y would anyone want a RAM disk on a Vax? ... you should >> increase your cache ... If your problem is in BACKUP, try using ... If this >> isn't the problem, please try and describe it more clearly, and maybe someone >> on INFO-VAX can help. >While I have no doubt that there is probably a reasonable (or maybe >unreasonable but at least fun) application for such a beast out there (which is >what I find really neat about working in this business), I would hope that >nobody is so innocent as to start putting a DBMS on it. I sure hope not. VMS treats the RAM (or pseudo)-disk like a floppy. Without looking at the source of the driver (PDDRIVER) I can't say for sure, but it's possible the a read from the pseudo-disk moves each character, one at a time, from the requested block of the pseudo-disk to an I/O buffer. I'm told that's what floppies do, and when I was using a pseudo-disk to boot standalone backup on a 785, it seemed about the same speed as the console floppy - can you say S...L...O...W ? >The fact that someone at DEC took the time to implement it and that it >is used in STABACKIT.COM is, I think, an indication that there is a niche >for it. > There is indeed! When booting standalone backup into a Microvax from the TK50, a pseudo-disk is created, standalone backup is copied into it, and then the Microvax continues booting from the RAM disk. If you use this subterfuge, you can remove the TK50 you booted from, put in another, and back up your system disk onto it. Standalone backup knows what device it was booted from, and it won't let you write onto what it thinks is your system disk. When booted from a TK50, standalone backup believes it was booted from the pseudo-disk, NOT the TK50. So it will let you write onto the TK50. It's also a neat way of getting around the assumption built into VMS that disks are the only bootable devices. Ever tried booting a TU81? With a pseudo-disk it should be possible. If anyone out there can make it work, please let the rest of us know! - Jonathan. -- ACSnet: jonathan@vuwcomp.nz UUCP: ..{alberta,ucb-vision}!calgary!vuwcomp!jonathan -- Murphy's Law: ``If anything can go wr Segmentation error (core dumped)