Messages in this thread | | | From | Badari Pulavarty <> | Subject | Re: 2.5.66-mm3 - bad ext2 performance ? | Date | Tue, 15 Apr 2003 16:17:08 -0700 |
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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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