Last week's "Windows Server 2003 better than Linux" test

[jra at dp.samba.org]

On Mon, May 12, 2003 at 03:52:10PM -0400, David Collier-Brown -- Customer Engineering wrote:
> jra at dp.samba.org wrote:
> > Hmmm. To be honest I think this is due to the Solaris UFS 
> > behavour - it seems to be very sensitive to write sizes
> > (that's why I added the write cache code). Linux doesn't
> > seem to need this as the kernel does the buffering.
> 
>    Yes, I can confirm that in part: up to 8 update 3 UFS (actually
> an updated ffs, not the old old ufs) wasn't particularly good at
> coalescing writes.
>    That changed a lot about then, and I found in traces that
> ufs was putting together some very nice large chunks. However,
> that mostly avoids small fragmented writes and excess seeks.
> Handing ufs multiples of the (block size * stripe width) is
> still a **very** good thing on a filesystem residing on
> a RAID array.
>    On a brand new filesystem, unrelated to ufs, the same is
> still true: RAID and big buffers beats ufs and small ones
> by ten to one.
>    And it applies to read as well: reading large amounts
> gets a lot of parallelism on the initial reads, and uses
> the readahead well thereafter.
> 
> [Just FYI: I've changed my strategy so that samba reading from
> a readahead cache so as never to give a "short read", and
> the code got simpler...]

Can you send me a patch for the read cache code. I'd like
to get this into 3.0 if possible.

>    A question for the Linux aficionados: can the OS get
> knowledge of the "best size" for RAID devices from the device?
> That sound like something a filesystem might be able to know
> and use...  albeit not ufs (;-))

Nope - no syscall I think.

Jeremy.