Re: [Xen-users] very slow disk access

[Randy Katz <rkatz@xxxxxxxxxxxxxxxxxxxxx>]

On 2/26/2011 5:24 PM, Fajar A. Nugraha wrote:
> On Sun, Feb 27, 2011 at 8:16 AM, Randy Katz<rkatz@xxxxxxxxxxxxxxxxxxxxx>  wrote:
> > On 2/26/2011 4:41 PM, Fajar A. Nugraha wrote:
> > > On Sat, Feb 26, 2011 at 11:20 PM, Randy Katz
> > > <rkatz@xxxxxxxxxxxxxxxxxxxxx>    wrote:
> > > > # lsmod | egrep "piix|hci"
> > > > ahci                   69705  7
> > > > ata1: SATA max UDMA/133 abar m2048@0xff970000 port 0xff970100 irq 253
> > > > ata1.00: ATA-8: ST31500341AS, CC1H, max UDMA/133
> > > > ata1.00: configured for UDMA/133
> > > A quick glance seems to show no driver problems. Did you experience
> > > any problem? Is your problem xen-specific?
> > I have very slow access in Xen for file based access. If I use LVM volumes
> > it is quite fast.
> Then why didn't you say so in the first post? It shouldn't be related
> to drivers. using file-based images are known to be slow or unreliable
> in some circumstances.
>
> > Using the same machine with OpenVZ
> > has no problems and performance is great.
> OpenVZ has different method to provide guest filesystem.
>
> > Will go ahead and use LVM volumes
> > and assume Xen likes them! :) Not sure what
> > else to do or look at, any comments?
> If you still need file-based image, try using non-sparse image and use
> tap:aio instead of file:/
> Stick with LVs whenever you can though.
it seems I am using tap:aio on what appears to be quite slow:

disk = [ "tap:aio:/disk0/server3.img,xvda,w" ]

Is there a good way to convert from tap:aio to lvm? I tried stop vm, dd 
if=server3.img of=/dev/vg1/newlv3
but it is very very slow, much quicker to blow away the whole thing (vm) 
and reinstall and then add data
from backups.

Regards,
Randy

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