On 11/18/2013 03:30 AM, Gene Czarcinski wrote:
On 11/17/2013 03:23 PM, Chris Murphy wrote:
So I'm trying to preallocate a VM image file using dd and I'm getting
a weird hang regardless of file system (XFS and Btrfs so far).
Existing shells, local and ssh, are very sluggish but work. I can't
create new shells, either local or ssh, they time out. This is the
command I'm using:
dd if=/dev/zero of=fedoraA.img bs=1M count=40000
Two questions here:
1. Have you tried bs=1K count=40000000 to see if it makes a difference?
2. What does filefrag show when you are done (especially on btrfs)?
I do assume that on btrfs you are doing "the right thing" and setting
chattr +C for the directory.
It takes between 10 seconds and 1.5 minutes for e.g. ls -lsh to
return results. And lsattr has been hung for 5 minutes and doesn't
return results until dd is done.
free -m reports around 100MB of free memory. There's no obvious
runaway process reported by top. So I'm not sure why there's this
much of a drag.
How to go about troubleshooting this?
OK, now some addition info ... what is the hardware/software?
I just ran your "problem" with no problem at all.
Hardware: i5-4570S, 16GB memory, twin 250GB SSDs
Software is F20-Beta with BTRFS volume on the SSDs data=raid0,
metadata=raid1,
/var/lib/libvirt/images as its own subvol,
chattr +C /var/lib/libvirt/images
While dd was running, I was able to do ls -lh and lsattr in another
window.
Oh, and ended up with 32 extents.
I would try playing with the file size and the block size to see what
difference it makes (if any). Right now, I (for one) cannot duplicate
your problem.
One other little thing, are you getting any disk errors? Did you try
running gnome-disks and look at the SMART data?
Gene
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