From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: 4.2.1: Poor write performance for DomU.
Date: Tue, 12 Mar 2013 09:04:30 -0400
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> >So still filesystem. Fio can do it on a block level.
> >
> >What does 'xenstore-ls' show you and 'losetup -a'? I am really
> >curious as to where that file you are providing to the guest as
> >disk is being handled via 'loop' or via 'QEMU'.
> >
> 
> I've picked out what I believe is the most relevant from xenstore-ls
> that belongs to the DomU in question:

Great.
.. snip..
>        params = "/dev/vg_raid6/fileshare"
>        mode = "w"
>        online = "1"
>        frontend-id = "1"
>        type = "phy"
>        physical-device = "fd:5"
>        hotplug-status = "connected"
>        feature-flush-cache = "1"
>        feature-discard = "0"
>        feature-barrier = "1"
>        feature-persistent = "1"
>        sectors = "5368709120"
>        info = "0"
>        sector-size = "512"

OK, so the flow of data from the guest is:
	bonnie++ -> FS -> xen-blkfront -> xen-blkback -> LVM -> RAID6 -> multiple disks.

Any way you can restructure this to be:

	fio -> xen-blkfront -> xen-blkback -> one disk from the raid.


to see if the issue is between "LVM -> RAID6" or the "bonnie++ -> FS" part?
Is the cpu load quite high when you do these writes?

What are the RAID6 disks you have? How many?