Date: Mon, 08 Sep 1997 10:42:52 +1000 From: Mike Smith <mike@smith.net.au> To: Greg Lehey <grog@lemis.com> Cc: 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: <199709080043.KAA00598@word.smith.net.au> In-Reply-To: Your message of "Sun, 07 Sep 1997 17:11:10 %2B0930." <19970907171110.27847@lemis.com>
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> > If you compare a 14" disk pack from the mid-seventies (SMDE) to a disk > > drive of today, you see that capacity climbed nicely (about 30x), > > performance has barely moved (I am NOT talking about 5MB Shugart 5.25"!), > > being that a good SMDE drive could do about 5MB/sec or even better, while > > CPU's jumped almost 300x! > > 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. You're talking IBM DASD here? I'll have to go beat up on the old man for more data here, but seeing as he bought several of most of that family over time (starting in about 1972) I would hope he could remember. 8) 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). The later ESMD disks were pretty hot performance-wise (eg. the Fujitsu Super Eagle and its successorss), the biggest limitation with those disks was the amount of power on the controller. Eg. the Emulex QD-32 used a single 8031. Later controllers (eg. Xylogics 451, Interphase 4xxx) had more CPU and more smarts, but even then they had sophisticated scatter-gather and request sorting algorithms. ... > This may sound funny until you look at the data transfer rates > involved. On the TXP, it was 240 kB per second, on the NonStop II it > was 120. Raw disk rate. Digital's SDI talking to an RA-81 was good for about 200K/sec; ESMD was much faster. > Sounds like a 1 GB RAM to me. Still cheaper per byte than any disk > made up to about 5 years ago. Yup. And if someone can work out how to deal with the power dissipation, a slab of pseudo-static RAM the size of a 3.5" drive will probably be cost-comparable inside the next 5-10 years. mike
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