Whether using the pv devices or the emulated ones should hardy make a
difference with respect of the timeouts and data loss which is reported
here. It has a performance benefit for the communication between the
instance and the Xen host, though. And we are about to release kernel
updates to have the required drivers built-in and not as modules (like
they are now). But those are currently in testing (for 11.04 and 11.10).

For the timeouts, I wonder whether that could be an effect of storage on
ec2 usually being network attached, together with a high(er) general
utilization. Actually moving from emulated to pv devices could make that
even worse. Surely there also is a chance that the pv driver handles
such delays/contention better than the emulated device driver.

But it should be possible to switch to the pv drivers even with the
current images. Just add the pci-platform, xen-netfront and xen-blkfront
drivers into /etc/initramfs-tools/modules, then run update-initramfs -u
and make sure that the root device in /boot/grub/grub.cfg and /etc/fstab
is using uuid or labels (because on reboot with pv drivers enabled
device names will switch from hd to xvd for the block devices).

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https://bugs.launchpad.net/bugs/704022

Title:
  xen_emul_unplug=unnecessary on kernel cmdline is required in ec2 hvm

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