[Xen-users] Slow Network Speed with CentOS 4 Guest

[Michael <asurfer@xxxxxxxxxxxx>]

Hello.

I have three Dell 2950 servers - two Xen machines - xen01 and xen02 - 
and one that is used to store backups. Each server has a pair of l quad 
core CPU's, the same SAS disk drives and firmware versions (BIOS, SCSI 
controller, onboard NIC and BMC).  The only way that they differ is that 
one server (xen01) currently has 12GB of RAM while the other 2 have 16GB 
of RAM.
With regards to the software that is installed on xen01 and xen02:

OS: CentOS 5.5 64 bit
kernel: 2.6.18-194.17.1.el5xen
xen version: 3.0.3.105.el5_5.5

So with regards to xen01:  It currently has 3 paravirtualized (PV) 
guests on it with each guest running CentOS 4.8 32 bit and Xen kernel 
version:
kernel-xenU-2.6.9-100

Now, with regards to file transfer speeds on the xen01 host and its guests:

xen01
=====
Dom0 <- backup server:       30MB/s
DomU (any) <- backup server: 30MB/s
DomU (any) <- DomU (any)     30MB/s
DomU (any) <- Dom0           23MB/s

So no problems there.

Now, xen02 currently has two PV guests on it: A CentOS 4.8 32 bit guest 
and a CentOS 5.5 64 bit guest and so with regards to file transfer 
speeds for the xen02 host and its guests:
xen02
=====
Dom0 <- backup server:             30MB/s
DomU (CentOS 4) <- backup server:   4MB/s
DomU (CentOS 5) <- backup server:  23MB/s
DomU (CentOS 5) <- DomU (CentOS 4) 23MB/s
DomU (CentOS 4) <- DomU (CentOS 5)  4MB/s
DomU (CentOS 5) <- DomU (CentOS 4) 23MB/s
DomU (CentOS 4) <- Dom0            23MB/s
DomU (CentOS 5) <- Dom0            30MB/s

Now the obvious problem here is the CentOS 4 guest on xen02.  The 
difference between the three CentOS 4 guests on xen01 and the CentOS 4 
guest on xen02 is that the three guests on xen01 each started off as 
separate machines and were upgraded over the years from CentOS 4.2 to 
CentOS 4.8.  So not too long ago, we decided to decommission those three 
old servers (the hardware that is) and so performed a bare metal restore 
of each three of those servers from the backup server to xen01.  
However, in the case of the CentOS 4 guest on xen02: It was simply being 
created and installed as a CentOS 4.8 guest straight onto xen02 (using 
virt-install).
Other things that I have checked are that all software versions and 
firmware are the same between both servers and that the output of :
ifconfig -a
brctl show

(ignoring the different MAC and IP addresses of course) are the same 
when comparing xen01 and xen02 and are the same when comparing between 
the CentOS 4 guests and that:
/etc/sysconfig/network-scripts/{ifcfg-eth0,ifcfg-eth1}
/etc/sysconfig/hw.conf
/etc/sysconfig/network
/etc/modprobe.conf
/etc/xen/*

are identical when comparing between both xen01 and xen02 and are also 
identical when comparing between the CentOS 4 guests (except for the MAC 
and IP addresses of copurse), I am totally at a loss here as to why the 
CentOS 4 guest on xen02 has such atrociously low speeds when 
transferring files from the backup server (and also from the CentOS 5 
guest on the same server - but I don't really care about that other than 
it may provide some sort of clue).
Another clue is that if I boot a Rescue CD such as the latest version of 
R.I.P. Linux where HVM has to be used, the transfer speed from the 
backup server to the R.I.P. Linux guest is also a paltry 4MB/s.
So if anyone can provide me with some clues or information as to how to 
improve on this 4MB/s speed problem both with the CentOS 4 container as 
well as with the rescue CD, then I would be most grateful as this 
problem has been driving me nuts.
Cheers,
Mike.


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