Current status.
New laptop hard drive purchased and installed.
Experiment 1
Instead of LVM with full disk encryption, have used LVM without full disk encryption.
Instead of transferring file to the lv used for DomU '/', have created a new lv mounted with 'mount /dev/xvda3 /mnt' insided DomU to use for transferring data to.
Result: 4.9Gb file transferred fine!
Experiment 2
Change from above (1): tried transferring to same lv as DomU's '/'
Result: successful transfer.
Experiment 3
Change from above (2):
LVM with Full Disk Encryption
data transferred to root filesystem.
Result: md5sum fails, failure.
Experiment 4
Change from above (3):
experiment trying to disable barriers, with no luck. Tried booting with rootflags=barrier=0, putting barrier=0 in /etc/fstab. None of these prevented seeing blkfront: xvda2: barriers enabled in the kern.log. Couldn't proceed further.
Discussion:
file sizes are always correct, which is interesting.
Seems that full disk encryption is the culprit.
What's next?