Re: Dealing with a very large file -1,5TB

[Christoph Klocker <cklocker@xxxxxx>]

Can you tell me how to make the lmdd direct=1 option to work,

I found your previous post, but don't know how to use that information
you can add the -D_GNU_SOURCE option to the cc options and it will get 
build with
direct I/O support direct=1
christoph

Steve Lord wrote:

> On Thu, 2003-09-25 at 11:16, Nathan Straz wrote:
>  
>
> > On Thu, Sep 25, 2003 at 05:20:23PM +0200, Christoph Klocker wrote:
> >    
> >
> > > then I did the benchmark how they were described in the man page I found on
> > > the web.
> > > [root@localhost lmdd]# ./lmdd if=internal of=/raid/XXX count=1000 fsync=1
> > > 8.1920 MB in 2.2116 secs, 3.7041 MB/sec
> > >
> > > unmounted and mounted again
> > > [root@localhost lmdd]# ./lmdd if=/raid/XXX of=internal
> > > 8.1920 MB in 0.0776 secs, 105.6065 MB/sec
> > >
> > > the 105 MB/s seem to be very slow, 
> > >      
> > I find that you really have to increase the block size you're using for
> > I/O.  Try adding "bs=1024" or similar to your command lines.  Also try
> > "odirect=1."
> >    
>
> bs=128k or some other larger value might be more meaningful. It looks
> like it is defaulting to 8K I/O buffers. A file size of 8M is going
> to be completely in cache when you read it back, so you are looking
> more at memory speed than anything else here. lmdd is part of lmbench,
> this contains tools to measure memory bandwidth too, if your memory
> bandwidth is going somewhere else, you need to do some investigation.
>
> Just using a simple scsi disk:
>
> lmdd if=internal of=fred count=1000 fsync=1
> 8.1920 MB in 0.4958 secs, 16.5234 MB/sec
>
> lmdd if=fred of=internal
> 8.1920 MB in 0.0355 secs, 230.9753 MB/sec
>
> adding O_DIRECT:
>
> lmdd if=fred of=internal direct=1
> 8.1920 MB in 0.4241 secs, 19.3180 MB/sec
>
> and on output, demonstrating differing buffer sizes with direct I/O
>
> lmdd  if=internal of=fred count=1000 fsync=1 direct=1
> 8.1920 MB in 2.4649 secs, 3.3234 MB/sec
>
> lmdd  if=internal of=fred count=1000 bs=32k fsync=1 direct=1
> 32.7680 MB in 3.6736 secs, 8.9200 MB/sec
>
> lmdd  if=internal of=fred count=1000 bs=128k fsync=1 direct=1
> 131.0720 MB in 7.7335 secs, 16.9487 MB/sec
>
> lmdd if=internal of=fred count=1000 bs=256k fsync=1 direct=1
> 262.1440 MB in 14.2395 secs, 18.4096 MB/sec
>
>
> Steve
>
>