[mythtv-users] LVM Issue with zero-length files

[Larry K]

Calling all LVM experts!!

Up until recently, I had been running LVM with only a single physical
volume. I probably have 100GB of data files in the volume, waiting to be
watched. So, Myth was running fine and all was well, except I had a 150GB
partition just laying around, not in use. So, I decided to extend my volume
group and add this 150GB to it, like so:

   1. Using fdisk, deleted /dev/hda4 partition
   2. Using fdisk, created /dev/hda4 as LVM
   3. Created physical volume: pvcreate /dev/hda4
   4. Extended volume group: vgextend vg /dev/hda4
   5. Ran vgdisplay to see amount of free space that needs to be extended
   (18214)
   6. unmount the volume group: umount /dev/vg/video
   7. extend: lvextend -l +18214 /dev/vg/video
   8. mount /dev/vg/video
   9. grow the xfs file system: xfs_grow /dev/vg/video
   10. Remove /video from /etc/fstab

Now, df -k shows the new space:

[root at mythtv ~]# df -k
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/hda2 10080520 2938120 6630332 31% /
/dev/hda1 101086 16752 79115 18% /boot
none 257908 0 257908 0% /dev/shm
/dev/mapper/vg-video 442105856 113816336 328289520 26% /video2

Everything appeared to be OK. I now had a 450GB partition for myth, instead
of 300GB. However, I soon discovered that new files are written with a
length of zero (empty files). Doh! The mythfrontend was able to play back
the existing files that were in the VG, but if I tried to delete a file, the
frontend would hang. That's when I knew I had a problem for sure.

Also odd is that when, as root, I cat /dev/video0 > /video2/xxx.mpg, this
file is also empty. However, if I copy an existing file, as in

cp /video2/blah blah.nuv /video2/xxx, it shows up with the proper length. So
old files copy correctly, but new files are not written correctly.

WTF?

There are no error messages in either the myth logs, nor the log file at
/var/log/messages.

I did notice that one of the HDs is running DMA 100, while the other is DMA
133. Does this matter to LVM?

Anyone have any thoughts as to what might be causing this? I am totally
stumped. If there is a way to back out and shrink the VG back to 300GB to
fix this, I'm all ears!
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