[Xen-users] poor network performance?

Kirchy
Tue, 28 Jun 2005 18:42:47 -0000

I played around with Xen before and now wanted to make serious use of it
for the first time:

I installed Xen on a p4-2.6ghz, 2GB RAM and SATA-disks (debian linux)
I set up an guest with debian sarge with no problems on a seperate
200gb-partition (as /).

I then tried to copy a large file (300mb) via scp and ftp from my main
database-server to the xenU (gigabit network, server is a opteron on a
high-end tyan-board with LAN on board, xen-pc is a intel-board with
gigabit-lan on board) to have an idea of how long it would take to copy
a large backup file via the network, but copying was so slow (around
4MB/sec), that i thought the ethernet-card might be in 100mbit-mode -
but it wasn''t. I have the same poor performance no matter if I copy to
dom0 or domU :(
I copied the same file to another database-server in the gigabit-network
and got around 12mb/sec (still slow, but that other database is under
heavy load so a lot of traffic should be on there)
I have acceptable performance when I copy a 300mb-file locally on the
xen0 from one sata-disk to another (16mb/sec). (time cp /tmp/file.dat
/disk2/file.dat)
I have around 9mb/sec if I copy a 300mb-file locally on xenU (time cp
file.dat file2.dat) on the same partition

I found out that eth0 on the xen0 was in promiscuous mode (because of
xen or the bridge utils?) and disabled that ( ip link set eth0 promisc
off), but the speed didn''t change.

Any ideas somebody? We''ve been using that Server with the same hardware
before as a backup system and didn''t have any performance problems.
When I start the server with the standard debian 2.6.7-kernel, I get
around 12mb/sec, so it must be about the xen-kernel?

Thanks for any hints... I''m stuck and confused right now..

Jan

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