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Re: [Xen-devel] Xen and iscsitarget

To: Nathan Lutchansky <lutchann-xendevel@xxxxxxxxxx>
Subject: Re: [Xen-devel] Xen and iscsitarget
From: Alvin Starr <alvin@xxxxxxxxxx>
Date: Thu, 04 Nov 2004 14:03:27 -0500
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Nathan Lutchansky wrote:

Hi all,

I've been using Xen for a few months now and I'm quite impressed.  Not
only is the virtualization platform stable and well-designed, but the
surrounding administrative tools and processes are usable and complete.
(Although I admit, I was kind of disappointed with the performance until I
realized recently that I hadn't compiled support for my ATA chipset into
the dom0 kernel and all disk I/O was PIO.)

My problem is that I'm unable to get the Cisco linux-iscsi initiator running under Xen. It seems other people have been able to do this so maybe I'm doing something wrong.

I'm running the Xen 2.0 release candidate (which, BTW, is very nice otherwise, I've had no other problems) and have iscsitarget 0.3.4 running on an external host. The iscsitarget has been working fine with non-Xen hosts.

Unfortunately, I'm unable to get unprivileged domains to talk to the iscsitarget. Using Linux 2.4.27-xenU with linux-iscsi 3.6.2 I get the error "xmit_data failed to send 8240 bytes, rc 48", and using Linux 2.6.9-xenU with linux-iscsi it simply locks up the whole kernel on session initiation. (Pings still work though.)

In domain 0, I can use linux-iscsi- to talk to the target successfully, however, under load I will often get syslog messages "iscsi-tx: page allocation failure. order:0, mode:0x20" and a big call trace (see below). These apparently cause no real problems though, and all my data seems to be intact and the filesystem works fine.

Domain:     Kernel:        Linux-iscsi:     Result:
unpriv      2.4.27-xenU    3.6.2            "xmit_data failed"
unpriv      2.6.9-xenU         immediate lock-up
domain 0    2.6.9-xen0         works fine, with strange errs

The lock-up with 2.6.9 happens after less than a kilobyte of data has been transmitted in either direction.

My unprivileged domains otherwise work fine and I've pumped many gigabytes of data between them and the network.

Since this only breaks from an unprivileged domain, I'm guessing that there's some incompatibility between how VIFs are implemented and how linux-iscsi wants to use them.

Can anybody suggest kernel and linux-iscsi versions that seem to work correctly? -Nathan

I am running a Fedora Core 2 as the OS on disk for Xen0
The /proc/version string is: Linux version (root@xenmaster1) (gcc version 3.3.3 20040412 (Red Hat Linux 3.3.3-7)) #1 Fri Oct 15 17:47:44 EDT 2004
the version of iscsi is: iscsid version 4:0.1.10 ( 8-Oct-2004)

I am not saying that this is a fact but I have found that:
1) run iSCSI over gigabit ethernet only.
2) insure flow control is turned on for all the switches and NIC's
3) use only e10000 or sysconnect NIC's

I have had lots of weird problems with via-rhine and 100BT connecitons.

I am using the IET(iscsitarget) 0.3.2

I am importing 3 target sytemss as an array and having the XenU's do the actual raiding of them. So far So Good. Knock on wood. Keep my fingers crossed

Alvin Starr                   ||   voice: (416)585-9971
Interlink Connectivity        ||   fax:   (416)785-3668
alvin@xxxxxxxxxx              ||

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