Unix administration stuff that was hard to find out using Google and caused a lot of try and error. Hereby given back to the net...
|
|
Tweet |
Ubuntu 12.04 on Xen: blkfront: barrier: empty write xvda op failed
Submitted by Lars Windolf on 6. June 2012 - 17:52.
When you run Ubuntu 12.04 VM on XenServer 6.0 (kernel 2.6.32.12) you can get the following errors and your local file systems will mount read-only. Also see Debian #637234 or Ubuntu #824089.
blkfront: barrier: empty write xvda op failed blkfront: xvda: barrier or flush: disabled
You also won't be able to remount read-write using "mount -o remount,rw /" as this will give you a kernel error like this
EXT4-fs (xvda1): re-mounted. Opts: errors=remount-ro
This problem more or less sporadically affects paravirtualized Ubuntu 12.04 VMs. Note that officially Ubuntu 12.04 is not listed as a supported system in the Citrix documentation. Note that this problem doesn't affect fully virtualized VMs.
The Solution:
- According to the Debian bug report the correct solution is to upgrade the dom0 kernel to at least 2.6.32-41.
- To solve the problem without upgrading the dom0 kernel: reboot until you get a writable filesystem and add "barrier=0" to the mount options of all your local filesystems.
- Alternatively: do not use paravirtualization :-)
This "reboot until you get a
This "reboot until you get a writable filesystem" reminds of "have you tried to turn it off and on again". And then it all ends up in the question: Are talking about Windows, or? No? What? :-)
Save some time
Instead of rebooting over and over, boot to a live CD ISO (Not 12.04, obviously), mount the filesystem and edit etc/fstab directly.
Some corrections and simplification
The mount option is "barrier", not "barriers", and you don't have to reboot. Just remount:
# mount -o remount,rw,barrier=0 -t ext4 /dev/xvda1 /
# vim /etc/fstab #add barrier=0 to local filesystem options
# reboot
RE: Some corrections and simplification
Thanks for the hint. I fixed the typo! I remember remounting didn't work, but it is worth trying...
I also get a read-only issue
I also get a read-only issue in Xen with Debian Wheezy, and the kernel output shows:
blkfront: barrier: empty write xvda op failed
blkfront: xvda: barrier or flush: disabled
end_request: I/O error, dev xvda, sector 20454592
end_request: I/O error, dev xvda, sector 20454592
Buffer I/O error on device xvda1, logical block 2556568
lost page write due to I/O error on xvda1
Aborting journal on device xvda1.
EXT3-fs (xvda1): error: ext3_journal_start_sb: Detected aborted journal
EXT3-fs (xvda1): error: remounting filesystem read-only
and I've tried
sudo mount -o remount,rw,barrier=0 -t ext4 /dev/xvda1 /
[sudo] password for buildbot:
sudo: unable to open /var/lib/sudo/buildbot/0: Read-only file system
mount: cannot remount block device /dev/xvda1 read-write, is write-protected
I've also tried several way to run e2fsck. directly, or with "sudo shutdown -rF now", but it still refuses to mount the disk in r/w modes.
How do you avoid
How do you avoid paravirtualization? I need the write barrier, I don't need very high performance.
RE: How do you avoid
You avoid paravirtualization by not using the Xen kernel and boot using the stock kernel in the VM's boot partition.
Post new comment