David Hicks's questions

We run 10 servers, mostly cheap requisitioned desktop machines, all running CentOS 5.1 and Xen. All these 10 servers do is run Xen virtual machines. Someone switched off the power supply to the server cupboard and a couple of machines have fried harddisks and will no longer boot. No worries, all the virtual machine disk images have DRBD mirrored copies on different servers, I just need to start those up while I work on getting those two machines back up.

I've replaced the boot drive on each of them and re-installed CentOS, Xen and DRBD. However, after a reboot, the severs can all see their local DRBD devices just fine but report a status of "WFConnection" - waiting for connection - for the remote link. Each device reports as "Secondary/Unknown". I've checked:

• Each server has iptables configured correctly to let DRBD traffic through - this is definite, the iptables config file is from a central repository and is identical to what it was before the machines crashed.
• It's not a DNS problem, as each server has a fixed IP address and DRBD.conf uses those IP addresses directly, so DNS isn't even used. I've made sure the new installs use the same fixed IP addresses and hostnames as the original servers.
• Each server can ping the other one on all IP adresses used, no problem there. The server are all connected to the same switch.

Does anyone know why DRBD is still refusing to connect?

I have a number of Xen virtual machines running on a number of Linux servers. These VMs store their disk images in Linux LVM volumes with device names along the lines of /dev/xenVG/SERVER001OS and so on. I'd like to take regular backups of those disk images so I can restore the VMs in case we need to (the LVM devices are already mirrored with DRBD between two physical machines each, I'm just being extra paranoid here).

How do I go about this? Oviously the first step is to snapshot the LVM device, but how do I then transfer data to a backup server in the most efficient manner possible? I could simply copy the whole device, something along the lines of:

dd if=/dev/xenVG/SERVER001OS | ssh administrator@backupserver "dd of=/mnt/largeDisk/SERVER001OS.img"

...but that would take a lot of bandwidth. Is there an rsync-like tool for synching contents of whole disk blocks between remote servers? Something like:

rsync /dev/xenVG/SERVER001OS backupServer:/mnt/largeDisk/SERVER001OS.img

If I understand rsync's man page correctly, the above command won't actually work (will it?), but it shows what I'm aiming for. I understand the --devices rsync option is to copy devices themselves, not the contents of those devices. Making a local copy of the VM image before syncing it with the remote server isn't an option as there isn't the disk space.

Is there a handy utility that can synch between block devices and a backup file on a remote server? I can write one if I have to, but an existing solution would be better. Have I missed an rsync option that does this for me?

We're planning to buy a large color networked laser printer / photocopier / scanner device, something around the $10,000USD range. This, as standard, understands PCL (version 5e, I think). How do I ensure we get decent color reproduction from this device?

We have a Windows Server 2003 print server, on which I can see drivers for other network printers have an tab on their "properties" dialog named "color management". This lets you associate an ICC or ISM color profile file with a given device. I understand I can (quite cheaply - around $30USD) print out a test page from the device to send off to a lab and get back a color profile to associate with the device. Then, if I understand correctly, I can calibrate monitors with a coloromiter (something like the Pantone Huey) and ensure that what is seen on the screen is what comes out on the printer.

However, the printer sales people are also offering us a Postscript module for the printer at around another $1,000USD. Seemingly this gives "better" color reproduction, although that is about the most detailed explanation the sales people can give. We have Ghostscript installed on the print server, so if any applications can only print Postscript we can create a redirected printer with the Postscript interpretation being done by Ghostscript.

Can anyone explain what it is about Postscript that gives "better" color reproduction? What makes Postscript worth paying $1,000 for?