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!!!ntpdate(1) has no effect
Xen by default just uses the dom0's clock, which isn't updated within the domU's.  Either set <tt>/proc/xen/independent_wallclock</tt> to 1 (so that this domU has an indepedent clock from the host dom0, or set the clock in the dom0.

!!!Making a tape drive available to a guest via iSCSI
__This is specifically for ~XenSource's range of products, although the principles will of course work in other Xen implementations__

I recently had a scenario where I was replacing two Windows servers with ~XenServer guests.  This was fine, but we needed a way to backup to the existing SCSI DDS4 DAT drive.  After failing to make PCI passthrough work, I settled on the much nicer method of providing the tape drive via an iSCSI target on the ~XenServer Host (Dom0).  Here is how I achieved this.

Note 1: This is totally unsupported by ~XenSource

Note 2: I've used the ~XenSource terminology "host" instead of Dom0, as this applies to the ~XenSource commercial implementation of Xen.  It will probably work fine on OSS Xen, but you can just install the normal kernel dev packages and ignore the DDK stuff.

* Download the [Xen DDK|http://tx.downloads.xensource.com/products/ddk/index.php]
* The DDK is an ISO containing a VM with a development environment.  Import it to your Xen host, and start it.
* Download [iscsitarget 0.4.14|http://optusnet.dl.sourceforge.net/sourceforge/iscsitarget/iscsitarget-0.4.14.tar.gz] (you MUST use this version, as the patch for rawio support will not cleanly apply to 0.4.15) into your DDK VM.
* Download the patch for [rawio support|http://sourceforge.net/mailarchive/attachment.php?list_name=iscsitarget-devel&message_id=1170171101.2822.23.camel@localhost.localdomain&counter=1]  into your DDK VM (assuming you're saving it in /tmp)
* Now do the following:
<pre>
yum install kernel-devel bison flex
tar -zxvf iscsitarget-0.4.14.tar.gz
cd iscsitarget-0.4.14
patch -p0 < /tmp/raw.p
make
</pre>
* scp the entire iscsitarget-0.4.14 directory to your destination Xen host, and on that host do:
<pre>
yum install make gcc
cd iscsitarget-0.4.14
make install
mkdir /lib/modules/2.6.16.38-xs3.2.0.531.3960xen/kernel/iscsi
cp kernel/iscsi_trgt.ko /lib/modules/2.6.16.38-xs3.2.0.531.3960xen/kernel/iscsi
depmod -aq
</pre>

The last three steps are required because <tt>make install</tt> will not copy the kernel module correctly outside the target environment.

* Now edit your <tt>/etc/ietd.conf</tt> and configure the tape as per the following example snippet:
<pre>
Target iqn.2007-04.com.example:tape0
     Lun 0 H=1,C=0,I=6,L=0,Type=rawio
     Type 1
</pre>

* Save and do <tt>/etc/init.d/iscsi-target start</tt>
* Modify <tt>/etc/sysconfig/iptables</tt> to allow port 3060 tcp from the IP addresses running the initiator.
* Attach to the target using the initiator of your choice.

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Version 13, saved on Monday, May 21, 2007 12:33:15 pm by CraigBox
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