Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!ucbvax!agate!darkstar!snafu.Eng.Sun.COM From: lm@snafu.Eng.Sun.COM (Larry McVoy) Newsgroups: comp.os.research Subject: Re: Extremely Fast File Systems Message-ID: <5512@darkstar.ucsc.edu> Date: 27 Jul 90 22:33:13 GMT Sender: usenet@darkstar.ucsc.edu Organization: Sun Microsystems, Mountain View Lines: 63 Approved: comp-os-research@jupiter.ucsc.edu In article <5465@darkstar.ucsc.edu> craig@BBN.COM (Craig Partridge) writes: > >I'm curious. Has anyone done research on building extremely >fast file systems, capable of delivering 1 gigabit or more of data >per second from disk into main memory? I've heard rumors, but no >concrete citations. > >I'm interested because I think we'll need such fast file systems as >we build distributed systems over gigabit networks, and I'm somewhat >curious to learn what, if anything, has been done so far in this area. Why not: Drives --------------- Let's approximate a gigabit by 107 megabytes. Let's assume that a nice drive rotates at 7200 RPM, and has 64KB / track, and has the ability to read two heads at once (this is about twice as good as any commonly available drive such as SCSI, IPI, or XD). Let's do some math: 7200 revs / minute = 120 revs / sec = 8.33 milliseconds / rev. 64KB * 2 heads * 120 revs / sec = 15,360 KB / sec. This means that the most that you can expect from a drive like this is 15MB per second. This assumes that you have a filesystem that can run the drive at the platter speed (which isn't such a bad assumption - I run SCSI's at the platter speed with a hacked version of UFS). These numbers are wildly optimistic. I worked on super computer drives a couple of years ago and they could do 12MB / sec and drives cost about $75K each. I think you'll see cheap 2MB / sec drives in a year or two. It will be a long time before you see cheap 15MB / sec drives. Why not: Busses --------------- A good bus these days runs at about 80 MB / sec flat out. We can make them faster but it gets harder and harder to do so and give them any size. Why not: CPU speed ------------------ A Sun 4/490 is a reasonably fast machine. Moving I/O requires a copy. The 490 has copy hardware that maxes out at 25 MB / sec in the kernel and 14 MB / sec in user space. Conclusion: ----------- I think the answer is (a) yes, we've thought about it but (b) no it won't happen with any conventional hardware soon. I suspect that you'll need parallel busses, CPU's, and disks in order to get that kind of I/O. Furthermore, the I/O requests have to be large (megabytes) in orer to get all those parts working at the same time. You'll *never* see a magnetic disk that deliver > MB / sec timed over 10K. --- Larry McVoy, Sun Microsystems (415) 336-7627 ...!sun!lm or lm@sun.com