Re: File system compression, not at the block layer

From: Richard B. Johnson
Date: Fri Apr 23 2004 - 15:59:49 EST

On Fri, 23 Apr 2004, [iso-8859-1] Måns Rullgård wrote:

> "Richard B. Johnson" <root@xxxxxxxxxxxxxxxxxx> writes:
> > On Fri, 23 Apr 2004, Joel Jaeggli wrote:
> >
> >> On Fri, 23 Apr 2004, Paul Jackson wrote:
> >>
> >> > > SO... in addition to the brilliance of AS, is there anything else that
> >> > > can be done (using compression or something else) which could aid in
> >> > > reducing seek time?
> >> >
> >> > Buy more disks and only use a small portion of each for all but the
> >> > most infrequently accessed data.
> >>
> >> faster drives. The biggest disks at this point are far slower that the
> >> fastest... the average read service time on a maxtor atlas 15k is like
> >> 5.7ms on 250GB western digital sata, 14.1ms, so that more than twice as
> >> many reads can be executed on the fastest disks you can buy now... of
> >> course then you pay for it in cost, heat, density, and controller costs.
> >> everthing is a tradeoff though.
> >>
> >
> > If you want to have fast disks, then you should do what I
> > suggested to Digital 20 years ago when they had ST-506
> > interfaces and SCSI was available only from third-parties.
> > It was called "striping" (I'm serious!). Not the so-called
> > RAID crap that took the original idea and destroyed it.
> > If you have 32-bits, you design an interface board for 32
> > disks. The interface board strips each bit to the data that
> > each disk gets. That makes the whole array 32 times faster
> > than a single drive and, of course, 32 times larger.
> For best performance, the spindles should be synchronized too. This
> might be tricky with disks not intended for such operation, of course.

Actually not. You need a FIFO to cache your bits into buffers of bytes
anyway. Depending upon the length of the FIFO, you can "rubber-band" a
lot of rotational latency. When you are dealing with a lot of drives,
you are never going to have all the write currents turn on at the same
time anyway because they are (very) soft-sectored, i.e., block
replacement, etc.

Your argument was used to shout down the idea. Actually, I think
it was lost in the NIH syndrome anyway.

> --
> Måns Rullgård
> mru@xxxxxx

Dick Johnson
Penguin : Linux version 2.4.26 on an i686 machine (5557.45 BogoMips).
Note 96.31% of all statistics are fiction.

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