Messages in this thread | | | Subject | (reiserfs) Re: More on 2.2.18pre2aa2 (summary of elevator ideas) | Date | Wed, 13 Sep 2000 17:25:31 +0200 (MEST) | From | (Rogier Wolff) |
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> "Jeff V. Merkey" wrote: > > > > One important point on remirroring I did not mention in my post. In > > NetWare, remirroring scans the disk BACKWARDS (n....0) to prevent > > artificial starvation while remirring is going on. This was another > > optimization we learned the hard way by trying numerous approaches to > > the problem.
Don't you want to do it a megabyte at a time to prevent abyssimal disk-performance? (i.e. take the separate megabytes backwards, but do every megabyte forwards)
instead of for (b=max;b>0;b--) do for (bb=max-STEP;bb > 0 ; bb -= STEP) for (b=bb;b<bb+STEP;b++) (sloppy coding! this is pseudocde, don't copy-paste.)
I expect about 120 IO operations of say 4k (480k per sec) out of a disk if you read strictly backwards. While you can get about 18 IOs of 1Mb per second (18M per second) out of a disk that you run a (forwards) megabyte at a time.
The extra latency in the "elevator" is then the time to read a megabyte, about 50ms, which sounds acceptable to me.
Roger.
-- ** R.E.Wolff@BitWizard.nl ** http://www.BitWizard.nl/ ** +31-15-2137555 ** *-- BitWizard writes Linux device drivers for any device you may have! --* * Common sense is the collection of * ****** prejudices acquired by age eighteen. -- Albert Einstein ********
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