On Tuesday 15 April 2003 02:24 pm, Andreas Dilger wrote:
> On Apr 15, 2003 14:00 -0700, Badari Pulavarty wrote:
> > This is kind of extreem. But I have 1070 LUNS and I mkfs/mounted (ext2)
> > all these and running "fsx" on all of them.
> >
> > I see very bad IO rate on the machine. fsx with O_DIRECT seems to be
> > doing okay. Any ideas on why regular filesystem (buffered) IO sucks ?
> > I dont' see even cache increasing ..
>
> Depending on what parameters you have passed to fsx, it isn't necessarily
> going to be doing a lot of I/O. The default for the fsx I have is to max
> the file size out at 256kB (on average it will be about half of that), and
> you have 1070 instances running, so that agrees with the ~110MB of cache
> difference between O_DIRECT and non-O_DIRECT.
>
> Also, in the non-O_DIRECT case fsx will be doing reads from cache and not
> disk, so there is no reason to see anything in "bi". The writes may or
> may not be a problem, as fsx is "truncate happy", so some large amounts of
> data that are "written" are immediately truncated again. For O_DIRECT,
> everything is going straight to/from disk, hence much higher IO numbers.
>
> What you should really be checking is how many "ops per second" you are
> getting from fsx with and without O_DIRECT. It would be my guess that
> the O_DIRECT fsx is actually _slower_ because it is doing more I/O (and
> waiting for it to complete). Run each fsx with some fixed number of ops
> (-N <num ops>) and see how long it takes for both tests to complete.
Sure. Will do !!
Thanks.
Badari
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This archive was generated by hypermail 2b29 : Tue Apr 15 2003 - 22:00:37 EST