Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!samsung!uunet!zephyr.ens.tek.com!gvgpsa!gold!grege From: grege@gold.GVG.TEK.COM (Greg Ebert) Newsgroups: comp.sys.ibm.pc.hardware Subject: Re: ISA boards, EISA bus Message-ID: <1477@gold.GVG.TEK.COM> Date: 21 Sep 90 17:11:16 GMT References: <1990Sep19.233544.16757@hayes.fai.alaska.edu> <1471@gold.GVG.TEK.COM> Organization: Grass Valley Group, Grass Valley, CA Lines: 45 > I write: > >>What about disk controllers ? Sheesh, an AT bus-master can transfer about >>4 MB/sec, which is 2-3 times faster than the fastest hard-disk transfer >>rate. > marshall@wind55.seri.gov (Marshall L. Buhl) writes: >I'm certainly no expert at this, but what if you're data striping to a >whole bunch of disks? Compaq, Dell and Northgate (and maybe others) use >data striping in their new tower systems. I guess that might be a valid question, but most of the time involved in disk operations involves seeking. UNIX has a neato scheme where accesses are queued and sorted so that head movement is generally 'sweeping' instead of erratic as in FIFO requests. Adding yet another level of complexity, transfers to/from another drive(s) is/(are) done while other units are involved in seek operations. Watch the activity lamps on a multi-drive UNIX system; it's kinda trippy. I presume network servers would do the same. Maybe this is termed 'data striping' ? A 512 byte sector can be eaten or barfed in about 130-140 microseconds by an AT. Assuming an average access time of 15 milliseconds for a rather speedy drive, the transfer overhead is ~1%. Even a track-track access will take >5msec, so your overhead jumps to 3%. For network-server applications, my hunch is that an ISA controller will still be acceptable because the _maximum_ data rate for Ethernet is 10Mbits per second, or 1.25Mbytes/second (neglecting overhead) which is another bottleneck. Contrast this to ~4Mbytes/sec for an ISA (AT) bus-master. The trick is how the files are laid-out physically on the disk, and how multiple requests are handled. People do PhD dissertations on this stuff (no joke, it's a massively complex problem). [lawyer fodder] UNIX is a trademark (or other silly possession) of AT&T. ------------------------------------------------------------------------- ##### {uunet!tektronix!gold!grege} Register to vote, then ## | ## grege@gold.gvg.tek.com vote responsibly # | # # /|\ # Support the First Amendment, not the party that attacks it #/ | \# "I was, BANNED in the USA" - 2 Live Crew #######