Re: Very low disk performance on 5.x
From: Steven Hartland (killing_at_multiplay.co.uk)
Date: 05/02/05
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To: "Poul-Henning Kamp" <phk@phk.freebsd.dk> Date: Mon, 2 May 2005 21:43:57 +0100
----- Original Message -----
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
> 0. Does the user know enough about what he is doing.
Im no expert but then again Im not beginner either :)
>>1. Write performance being nearly 3x that of read performance
>>2. Read performance only equalling that of single disk.
>
> If the user expects an out of the box configuration with
> default parameters to give him maximal performance, the
> answer to issue number zero is: Obviously not.
Not maximal, that will never be the case, but reasonable yes and
it doesnt look like we are getting that ATM.
>>I'm quite willing to test and optimise things but so far no one has
>>had any concrete suggestions on that to try.
>
> First thing I heard about this was a few hours ago. (Admittedly,
> my email has been in a sucky state last week, so that is probably
> my own fault).
Hehe its been kicking around for a few days, might be of benifit
it you check back some some of the info posted by others.
>>This is just me though I think we do need to strive for good out
>>the box performance in these types of senarios
>
> We strive for a sensibly balanced system, no matter what use
> people put an out-of-the-box configuration to.
Indeed and I would classify this one of those such senarios.
>>> Testing end-to-end means that we have very little to go from to
>>> find out where things went wrong in any one instance.
>>
>>To eliminate various parts of the subsystems I've just tested:
>>dd if=/dev/da0 of=/dev/null bs=64k count=100000
>>Read: 220Mb/s
>
> This is a very interesting number to measure, you'll never
> see anything else going faster than that. Presumably
> this is -current ?
Nope thats 5.4-STABLE this should be at the very least
260Mb/s as thats what the controller has been measured on
linux at even through the FS.
>>Compared with:
>>dd if=/usr/testfile of=/dev/null bs=64k count=100000
>>Read: 152Mb/s
>
> On -current and 5.4 you don't have to make partitions if you
> intend to use the entire disk (and provided you don't want
> to boot from it). You can simply:
>
> newfs /dev/da0
> mount /dev/da0 /where_ever
Booting from it unfortunately. Although wasnt when running
the big set of tests results I reported ealier.
Gonna rip the machine out and put the test OS disk back in
and try that.
> This should have the sideeffect of aligning your filesystem
> correctly to the RAID volume.
>
>>So looks like the FS is adding quite an overhead ~70Mb/s ( 60% )
>>although from the linux tests we know the disks are capable
>>of at least another 40Mb/s
>
> Yes, filesystems add overhead. That's just the way things are.
To be expected but 60% overhead is a bit excessive.
> One thing you could try is to use a larger block/fragment size
> on your filesystem. Try:
>
> newfs -b 32768 -f 4096 /dev/da0
Will do.
>>> Did you remember to disable all the debugging in FreeBSD 6-Current ?
>>> (see top of src/UPDATING)
>>
>>Yep all debugging was disabled on my second run on current.
>
> Just checking: what exactly did you disable ?
Dont have it to hand any more witness etc, all the debugger options +
stripped out all the unneeded drivers.
>>N.B. Current had at least on out of order lock issue while I was using
>>it but not while the tests where going on.
>
> Yes, current is current :-)
As I thought hence its not running that any more bit to unstable for
my main dev box :)
Steve
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