[linux-lvm] Re: [Announce] device-mapper beta3 (fast snapshots)

[Chris Mason]

On Tue, 2002-07-16 at 12:31, Joe Thornber wrote:

> > Joe, are you absolutely sure these tests had the disk cache disabled?  That's
> > the only hardware thing I can think of that would make a difference.
> 
> Absolutely sure.  Those figures were for a pair of PVs that were
> sharing an IDE cable so I can certainly get things moving faster.

Some IDE drives ignore commands to turn off the write back cache, or
turn it back on when load gets high.

Try iozone -s 50M -i 0 -o with writeback on and off.  If you get the
same answer the benchmarks are suspect....

-chris