Re: [Xen-users] Bad iSCSI I/O performance on Xen 4.6

[Jean-Louis Dupond <jean-louis@xxxxxxxxx>]

Maybe an important addition:

I did some iperf testing on the 10G machines (on dom0), and we almost 
max-out the 10G link.
So it seems like the nic's are performing like they should.


On 08-10-18 13:10, Jean-Louis Dupond wrote:
> Hi,
>
> We are hitting some I/O limitation on some of our Xen hypervisors.
> The hypervisors are running CentOS 6 with Xen 4.6.6-12.el6 and 
> 4.9.105+ kernels.
> The hypervisors are attached with 10G network to the SAN network. And 
> there is no congestion at all.
> Storage is exported via iSCSI and we use multipathd for failover.
> Now we see a performance of +-200MB/sec write speed, but only a poor 
> 20-30mb/sec read speed on a LUN on the SAN.
> This is while testing this on dom0. Same speeds on domU.
>
> If I do the same test on a Xen 4.4.4-34.el6 hypervisor to the same LUN 
> (but attached with 1G), I max out the link (100MB read/write).
> On the same storage network we also have a bare metal machine, and 
> there we have 400-500MB/sec read-write performance on the same LUN!
> So it really looks like the Xen 4.6 hypervisors are reaching some 
> bottleneck. But we couldn't locate it yet :)
> The hypervisor's dom0 has 8 vCPU and 8GB RAM, which should be plenty!
>
>
> Anything we could try to improve the speeds?
>
> Thanks
> Jean-Louis

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