Your Linux Data Center Experts

I have a cunning plan to make a discless machine that boots via gPXE and iSCSI off the network from a machine in the basement. Preferably, accelerated with flashcache and an SSD. :-) So today I've been playing with setting up an iSCSI server, installing a distro to it, and then getting it to boot. Read below for some details about the configuration.

First off, my recommendation if you want to boot a machine entirely off iSCSI is to use Fedora 14 instead of Ubuntu Maverick. Fedora just worked right out of the box, but Ubuntu had issues and I was never able to get it to boot. After manually changing the initrd to remove the “(null)” it had put in for the username and password for iSCSI without passwords, I was getting the error “iscsi_trgt: scsi_cmnd_start(1045) Unsupported 85” on the iSCSI server and couldn't find a solution.

I created an LVM on top of the flashcache device I wrote about yesterday. I then created a 100GB logical volume which I configured “ietd” (the iSCSI target daemon) to export via iSCSI. That all went real smoothly.

Then on the client side when I did the install I just had to tell it to scan the server, and then select that exported device. At that point you can partition it and install GRUB just like it's a normal local device.

I already had gPXE set up, so all I had to do was add a stanza for the machine I wanted to iSCSI boot:

host iscsitest-atom
{
   hardware ethernet aa:00:c0:7f:4a:18;
   fixed-address 172.20.2.50;
   if exists user-class and option user-class = "gPXE" {
      filename "";
      option root-path "iscsi:172.20.2.49::::iqn.2010-11.com.example:sda.iscsitest";
   }
}

The real trick here was specifying the blank filename, because otherwise it was trying too boot up my PXE install menus. In other words, filename takes precedence over root-path. The “iqn” string is what I listed in my ietd.conf file, the .49 IP is my iSCSI server and .50 is the client. I gave it a fixed address just to make debugging a little easier.

Unfortunately, I'm running this on a fairly slow Atom box, so I don't get a very good feel for how the performance of the flashcache is going to be. I guess I should pull the drive from my laptop and do an install on it to see how performance is on a system I already am familiar with. But that's for another day.

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