[geeks] Cheap Dell Servers
mouse at Rodents.Montreal.QC.CA
Thu Feb 7 23:01:54 CST 2008
> But I thought the whole point of FFS's method of minimizing
> fragmentation was that when it goes to allocate the next sector it
> needs to allocate, it calculates what would be the optimal sector to
> allocate from based on the drive parameters, and if that sector is
> not free, it picks a free sector to allocate which is as close to
> optimum as possible (probably still in the same cylinder but on a
> different head or something)?
That's something FFS does, or at least tries to, yes, but it doesn't
have anything to do with fragmentation, as I understand fragmentation.
My understanding of FFS's way of dealing with fragmentation is just to
try to allocate files contiguously, and try to keep some 5-10 percent
of the space free so that this can usualy be done, or close enough to
>> I do know that using the disk-provided geometry does not produce a
>> system that feels significantly faster than using my usual 64
>> sect/trk 32 trk/cyl "1M cylinders" geometry, [...]
> My main concern in this exercise is to decode compressed HD video,
> which can be a bit sensitive to fragmentation at times, according to
> my own experience. If the difference in streaming video performance
> will be negligible, I won't worry too much about it.
I don't know; that's different enough from my kind of workload that my
experience probably means little. I'd recommend trying it; all the
opiniosn in the world aren't worth half jumping in and finding out.
(Well, at least when the experiment can be done without too much pain.)
> So, on ZBR drives, does it become wholly irrelevant? If so, I won't
> worry about what parameters are in my disklabels.
I'd hesitate to go so far as to say _wholly_ irrelevant, at least not
without actually trying it. (These things are complicated even further
by drives auto-sparing flaky sectors and the like, which can, from the
host poin of view, reorder sectors in a track; spare tracks mean that
similarly hidden seeks can be introduced beyond the host's control.)
But I do think that it's not worth worrying about unless you have some
experimental basis for thinking otherwise. Not that that's more than a
guess, albeit a slightly educated guess....
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