Date: Sun, 07 Sep 1997 21:48:56 -0700 (PDT) From: Simon Shapiro <Shimon@i-Connect.Net> To: Greg Lehey <grog@lemis.com> Cc: FreeBSD Chat <chat@FreeBSD.ORG> Subject: Re: lousy disk perf. under cpu load (was IDE vs SCSI) Message-ID: <XFMail.970907214856.Shimon@i-Connect.Net> In-Reply-To: <19970907171110.27847@lemis.com>
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Hi Greg Lehey; On 07-Sep-97 you wrote: ... > Well, I can't remember the performance of the mid-70s, but my > recollection of the performance in the early 80s on, say, a 3330 clone > was that these drives had 30 sectors (2 spares) per track, and they > ran at 3600 rpm. Since they weren't buffered, that gives a maximum > data transfer to the channel of about 860 kB/s. Average positioning > was round the 30 to 35 ms mark. Check out Priam 14" 60MB drives, check Floppy drives from the early 80's. They were all much faster than that. I clearly remember my Heathkit H8 seeking at 5-7ms on a 5.25" floppy. > At the time, I was working for Tandem. We noticed a puzzling > behaviour: our new flagship model TXP, whose CPU was about 100% faster > than the previous NonStop II, read data off these disks at almost > exactly double the speed of the NonStop II. Why? We finally figured > out that we were reading 4 kB blocks (the maximum our disk controllers > would allow), doing some processing, and then issuing the next read. > Unfortunately, on the NonStop II this took such a long time that the > head had passed the next block before it issued the read. In other > words, the "high performance" TXP managed to read a 4 kB block every > revolution, and the NonStop II needed two revolutions per 4 kB block. This is called inteleave factor. The semantics for 4.2bsd mkfs supported that feature. My CPM 1.1 IMSAI BIOS supported that on a floppy drive. We did, on a Z-80 machine of my design 256KB/sec from a single hard disk. Vax-780 did over 500KB/Sec in that time frame. We always knew Tandem was turtle slow. I finally have a witness to why :-) On the original Tahoe, we complained about 780KB/Sec and striped it to get more data out of it. ... > Again, I can't agree in the slightest. I *do* have the technical doc > for a 2311 drive floating around somewhere in the shed, and they were > unbelievably primitive. I may not remember some of the old numbers, but it is a rather well established fact that the difference in performance between CPU and external storage grows rapidly. My point was to exemplify it and encourage the young (at heart) and energetic to think in new ways. ... > Sounds like a 1 GB RAM to me. Still cheaper per byte than any disk > made up to about 5 years ago. Not necessarily so. What you refer to is DRAM, which loses its mind if not read in 2ms. Not exactly long term storage. ``Permanent'' storage is stil important. Remember that RAM was born as a compensator to off-line storage slowness. Originally there was a store and there were registers. RAM really is a non-entity from architectual point of view. It is a headache, that is true. The C language recognizes it as a viable entity, this is also true. But to the end-product functionality it is really non-entity. You always pass data through it, data is only useful in either storage or display. And these are really registers. > > will make more money than BG thought exists. > > Not if BG has anything to say in it. He is exactly where IBM was before him. To the Tee. Now see what happened to them. --- Sincerely Yours, (Sent on 07-Sep-97, 21:31:17 by XF-Mail) Simon Shapiro Atlas Telecom Senior Architect 14355 SW Allen Blvd., Suite 130 Beaverton OR 97005 Shimon@i-Connect.Net Voice: 503.643.5559, Emergency: 503.799.2313
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