Re: [linux-lvm] LVM, rawio, ext2?

[David Rees <dbr@greenhydrant.com>]

On Fri, Aug 24, 2007 at 11:31:36AM +0200, Dirk Heinrichs wrote:
> David Rees wrote:
> > 
> > Hi,
> > 
> > I'd like to create an ext2 filesystem over a raw io device, is this even
> > possible?  (If not, skip the rest of this message! ;-)
>
> Why do you want to do that?
> 
> These are two opposite things. One uses a raw device where an
> application has it's own storage layout, like databases.
> 
> If you just want to make shure that your files on an ext2 are written
> immediately, then mount with sync option.

Well, the version of Sybase I'm running (11.9.2) does not support Linux raw
partitions.  Sybase 12.5 reportedly does, but I have a number of servers
running 11.9.2 and don't want to upgrade yet.

Sybase 11.9.2 only supports database data put onto filesystems on Linux, so
I was hoping to create a situation where writes to the filesystem would not
be buffered by the operating system since Sybase has it's own buffers. 

Buffering IO to the filesystem also has the nasty side-effect of putting
increased VM pressure on the system and with 2.4.X kernels this leads to
poor performance.  (See the threads on linux-kernel describing huge
slowdowns with Oracle and 2.4.x when moving from 2.2.x).

Until I can validate my applications on Sybase 12.5 using rawio, I was
looking for a way to prevent filesystem IO from being buffered.

If anyone has any ideas, let me know!

Thanks,
Dave