[linux-lvm] Paralell IO performance with LVM and XFS

[Russell Coker]

On Thu, 17 Jan 2002 13:29, Miguel Angel de Vega wrote:
> I've a Dual P2 450 with a Disk Array with 4 scsi disks with XFS.
> With one single disc I've 10 Mb/s reading and writing, so I think that if I
> stripe all disc of the array, it can give me 4x10Mb = 40Mb/s more or less,
> but I only gets 10 Mg/s!!

Striping across 4 disks will never give you 4* the throughput of 1 disk, but 
you would hope for double the throughput.

> These disks usually gives up to 30 Mg/s in SGI machines and other single
> scsi disks in the Dual P2 (with the same controller and XFS) gives 20Mg/s,
> so i think that the problem must be LVM (the options maybe??? bad stripped
> options??).

How are you testing the speed of the disks?

I suggest that you do the following:
Test an ext2 partition on a single unpartitioned disk.
Test an XFS partition on a single unpartitioned disk.
Test XFS on a simple LVM setup (single disk, single LV in the VG).
Test XFS on the 4 disk LVM setup.
Run 2 copies of the test program at the same time on XFS on the 4 disk LVM.
Run 4 copies of the test program at the same time on XFS on the 4 disk LVM.

Then send us all the raw data from the above.  NB Bonnie++ has good support 
for running 2 and 4 copies of the test at the same time.

Also for interest, run zcav (from the Bonnie++ package) on a raw disk to show 
the throughput of the disk (without a file system).

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