Very low disk performance on 5.x
phk at phk.freebsd.dk
Mon May 2 10:33:24 PDT 2005
In message <003901c54f36$0c64ad40$b3db87d4 at multiplay.co.uk>, "Steven Hartland"
>Ok from what your saying it sounds like RAID on FreeBSD is useless
>apart to create large disks. Now to the damaging facts the results
>from my two days worth of testing:
Now, cool down a moment and lets talk about what you _really_ have
You have measured the end to end performance: you include /dev/zero,
dd(1), filesystem, disk device driver, hardware and disks.
As such that is a fair end-user benchmark, but unfortunately it
doesn't really tell us anything useful for the purpose of this
If you are going to do a high-performance setup, you should not
just take the "out-of-box" settings, you should optimize for
the configurations particular features.
Testing end-to-end means that we have very little to go from to
find out where things went wrong in any one instance.
But anyway: here are some questions which I wonder about ?
Does the linux and FreeBSD filesystem offer the same semantics
with respect to integrity ? Ie: if one is asyncronous mode
the comparison is not a fair comparison. Just because you
chose the default in each case doesn't mean you got the same
Does any of the drivers change the settings/modes of the controllers
use of cache ? (this may be hard to determine without looking
at driver sources.
In particular, are you sure that the RAID-5 logical device was
in the same exact state and location for each run ?
Did you remember to disable all the debugging in FreeBSD 6-Current ?
(see top of src/UPDATING)
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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