Date: Mon, 08 Sep 1997 16:00:34 +1000 From: Mike Smith <mike@smith.net.au> To: Greg Lehey <grog@lemis.com> Cc: Mike Smith <mike@smith.net.au>, Simon Shapiro <Shimon@i-connect.net>, FreeBSD Chat <chat@freebsd.org> Subject: Re: lousy disk perf. under cpu load (was IDE vs SCSI) Message-ID: <199709080600.QAA01679@word.smith.net.au> In-Reply-To: Your message of "Mon, 08 Sep 1997 15:18:23 %2B0930." <19970908151823.35891@lemis.com>
next in thread | previous in thread | raw e-mail | index | archive | help
> >>> However, Simon is close; the ESMD spec allows for a data clock of 25MHz > >>> (the data separator is on the disk, not the controller, IIRC). > >> > >> Depends on the drive. > > > > What "depends" on the drive? > > The location of the data separator. Thinking about it, though, I'm > not sure I remember correctly. I was pretty sure we only had one read > data and one write data line, but I could have been wrong. Those > cables were about .75" thick. No, you're correct. The ESMD interface looks a lot like the ESDI interface (no surprises there, really); there's only one data line in each direction, and the separator is on the drive. > > The ESMD spec lays out the maximum clock rate for the data, and the > > separator has to be on the drive if you're going to claim to be > > ESMD. > > Well, I'm not even sure if the 3330 is ESMD. We called it SMD > (Storage Module Drive). What does the E mean? Extended? When did it > come out? IIRC, SMD maxed out at 10 or 15MHz. ESMD defined some more commands and supported increased data rates; I recall both 20 and 25MHz drives. > > I've had blood out of similar units on my hands (and blood out of my > > hands on similar units 8) and I get the distinct impression that > > multiple-head read activity was the norm. > > They may have been in the environment you're talking about. They > weren't at Tandem, and I'd guess that any multi-head stuff didn't come > until the mid-80s. Hmm. I confess that units prior to the late 70's would have been destroyed before I was old enough to understand their workings well, let alone remember them. > > Sure. I think your earlier point about the basic mechanical > > limitations is quite valid though; there's a basic restriction inherent > > in having to fling the head assembly around. Still... > > Sure. In fact, I'm astounded how much disk drives have improved in > the last 15 years. In 1982, Tandem introduced a 540 MB CDC SMD disk > drive, the disk drive for gluttons. It was a heap of shit. It Heh. I think this was the ancestor to the 515MB units that I remember so fondly. Did it make "whale noises" as part of its self-test? > that, we went to little 8" Fujitsus). Try and find a new production > disk drive *anywhere* with only 540 MB, 30 ms positioning, 800 kB/sec > transfer rate nowadays. By comparison, even the shittiest IDE drives > are a dream. Sounds like a Zip drive. 8) mike
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199709080600.QAA01679>