Re: [Xen-users] read from FC lun under Xen 4 - very strange behavior

[G.Bakalarski@xxxxxxxxxx]

Hi

Thanks for input.

I'll give a try to alpine later on.

Currently I discovered this is rather not related to FC but to all
block devices ....
I tested similar  reads on my internal PERC lvm volume (raid5 with 4 disk
device) and basically it has the same problem i.e. write is stable
and fine but read is unstable and very frequently very slow...
It randomly varies from more about 300MBytes/s (good) to
25MBytes/s (very bad).

Tested always from dom0. With different kernels (2.6.32-5-amd64,
3.1, 3.2, Xen 4.0, Xen 4.1).
Without Xen reads and writes perform perfectly. With
Xens very very strange ... There must be something very
rude overlooked ... This has to work correctly in thousands of
installations worldwide ...

Kind regards,

GB


> 2012/2/23  <G.Bakalarski@xxxxxxxxxx>:
>> THE PROBLEM is read performace. Without Xen hypervisor read performance
>> is stable and high e.g. streaming reading from Dell LUN with Xen with
>> speed about 420MBytes/s (under iostat I can see speed in a range
>> from 390MBytes/s up to 450MBytes/s)
>
> can you please try the same test with a non-Debian distro to find out
> if this is kernel related?
> I.e. the AlpineLinux dom0 ISO might be a very easy solution - although
> I've not used it in a SAN yet.
> Otherwise try Fedora16.
>
> If you can pin-point this as an issue in your dom0, then I think you
> should take it to -devel since you're only seeing it in (less CPU
> intensive) reads, which is *quite* odd.
>
> Greetings,
> Florian
>
> --
> the purpose of libvirt is to provide an abstraction layer hiding all
> xen features added since 2006 until they were finally understood and
> copied by the kvm devs.
>



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