Don't get me wrong,
but my first thought was: What is the maximum expected throughput of the
nfs server? It should at least be connected with 2 GBit/s to the switch,
to serve two dd's with each ~100MB/s.
Well, I assume both domU's are using the same nfs server.
Regards,
Stephan
tmac schrieb:
> I have a beefy machine
> (Intel dual-quad core, 16GB memory 2 x GigE)
>
> I have loaded RHEL5.1-xen on the hardware and have created two logical 
> systems:
> 4 cpus, 7.5 GB memory 1 x Gige
>
> Following RHEL guidelines, I have it set up so that eth0->xenbr0 and
> eth1->xenbr1
> Each of the two RHEL5.1 guests uses one of the interfaces and this is
> verified at the
> switch by seeing the unique MAC addresses.
>
> If I do a crude test from one guest over nfs,
> dd if=/dev/zero of=/nfs/test bs=32768 count=32768
>
> This yields almost always 95-100MB/sec
>
> When I run two simultaneously, I cannot seem to get above 25MB/sec from each.
> It starts off with a large burst like each can do 100MB/sec, but then
> in a couple
> of seconds, tapers off to the 15-40MB/sec until the dd finishes.
>
> Things I have tried (installed on the host and the guests)
>
> net.core.rmem_max = 16777216
> net.core.wmem_max = 16777216
> net.ipv4.tcp_rmem = 4096 87380 16777216
> net.ipv4.tcp_wmem = 4096 65536 16777216
>
> net.ipv4.tcp_no_metrics_save = 1
> net.ipv4.tcp_moderate_rcvbuf = 1
> # recommended to increase this for 1000 BT or higher
> net.core.netdev_max_backlog = 2500
> sysctl -w net.ipv4.tcp_congestion_control=cubic
>
> Any ideas?
>
>
-- 
Stephan Seitz
Senior System Administrator
*netz-haut* e.K.
multimediale kommunikation
zweierweg 22
97074 würzburg
fon: +49 931 2876247
fax: +49 931 2876248
web: www.netz-haut.de <http://www.netz-haut.de/>
registriergericht: amtsgericht würzburg, hra 5054

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