[linux-lvm] lvm lowers transfer rate

[Patrick Caulfield]

On Wed, Jul 24, 2002 at 09:16:36PM -0400, Innocent Azinyue Ndangoh wrote:
> 
> Hi there,
> 
> I have 4 fiber channel disks, on which I intend to build a logical volume 
> using lvm. Before creating the logical volume, I run an I/O test on the 
> disks, which revealed that the disks each would do 10MBytes/sec I/Os.
> 
> However, when I create a logical volume, spanning all 4 disks using RAID0, 
> I realize that the transfer rate now drops. Instead (10 * 4)MB/s, I get 
> something close to 30MB/s. Am I doing something wrong?!?

I have found that striping Fibre-Channel only gives a performance boost up to
3 disks. I'm not sure whether that's a restriction of the FC interface I'm using
(emulex) or the Linux driver but it's certainly consistent with what you're seeing.

patrick