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Benny Baumann wrote:
<blockquote cite="mid:4AD39320.9030100@geshi.org" type="cite">
<pre wrap="">Am 12.10.2009 20:33, schrieb Thorsten von Eicken:
</pre>
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<pre wrap="">Thorsten von Eicken wrote:
</pre>
<pre wrap="">One further thought, instead of trying to allocate RRDs sequentially,
if there is a way to query/detect where each RRD file is allocated on
disk, then rrdcached could sort the dirty tree nodes by disk location
and write them in that order. I don't know whether Linux (or FreeBSD)
have a way to query disk location or to at least infer it.
TvE
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<pre wrap=""><!---->Even though Linux and Windows (and I guess most other OSes) allow to
query the "logical" disc position the physical location maybe completely
unrelated to this as modern harddrives mayreallocate certain sectors if
they feel that one particular sector cannot be read\written properly.
Thus trying to infer the physical location of data will not be accurate.
To take this even further not even the volume you write onto hast to
exist physically, e.g. you might have a RAID or LVM in which case one
logical sector corresponds to more than one physical location or as in
cases of a RAM disc none at all (at least no permanent one).
To make the picture complete there's even another factor that makes this
nothing you want to do in software: Modern harddrives usually "plan"
their read and write requests automatically already. So when write
accesses occure right behind each other the harddrive will already
figure out the best way to write them - unless you enforce synchronous
request completion with e.g. O_DIRECT or thelike.
</pre>
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Ben, I understand what you are saying. The question I have is not
whether it's always possible and meaningful to do this, the question is
whether it's possible to arrange this with the right set-up. Also, I
wouldn't be looking for 100% accuracy, even if it was only roughly it
could be a significant improvement.<br>
TvE <br>
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