goudreau@dg-rtp.dg.com (Bob Goudreau) (02/14/90)
In article <4882@amelia.nas.nasa.gov> truesdel@sun217..nas.nasa.gov (David A. Truesdell) writes: >In addition, a mirrored filesystem won't help your I/O throughput. Actually, that depends on the system's read/write ratio. Writes to a mirrored file system obviously must result in I/O to each (valid) side of the mirror. But reads, on the other hand, only need to find *one* good copy. An intelligently implemented mirrored file system can increase I/O throughput by distributing read requests evenly among the copies, thus leaving the unused sides of the mirror free to service other incoming read requests. ------------------------ Bob Goudreau +1 919 248 6231 Data General Corporation ...!mcnc!rti!xyzzy!goudreau 62 Alexander Drive goudreau@dg-rtp.dg.com Research Triangle Park, NC 27709, USA
lm@snafu.Sun.COM (Larry McVoy) (02/14/90)
In article <47@xyzzy.UUCP> goudreau@larrybud.dg.com (Bob Goudreau) writes: >In article <4882@amelia.nas.nasa.gov> truesdel@sun217..nas.nasa.gov (David A. Truesdell) writes: >>In addition, a mirrored filesystem won't help your I/O throughput. > >Actually, that depends on the system's read/write ratio. Writes to >a mirrored file system obviously must result in I/O to each (valid) >side of the mirror. But reads, on the other hand, only need to >find *one* good copy. An intelligently implemented mirrored file >system can increase I/O throughput by distributing read requests >evenly among the copies, thus leaving the unused sides of the >mirror free to service other incoming read requests. Good point. Here's something else to consider though, when thinking about this sort of thing. When you speak of the read/write ratio, be careful to tell me which side of the buffer cache you mean. The read/write ratio on the system call side is about 4:1, but on the other side I've found it's much more like 1:4. In other words, the cache caches lots of reads, but the writes end up going through (most of the write traffic I've seen are directory updates since they are synchronous). Just a thought... --- What I say is my opinion. I am not paid to speak for Sun, I'm paid to hack. Besides, I frequently read news when I'm drjhgunghc, err, um, drunk. Larry McVoy, Sun Microsystems (415) 336-7627 ...!sun!lm or lm@sun.com