[rasp pi] can't make owncloud see an external HDD RAID 1

Officially stumped, asking for assistance.

Got a USB2.0 hub and created a RAID 1 (md0) drive out of 2 empty, ext4 drives. rsync'd over a bunch of data, unplugged a drive, dd'd some random 0's and 1's on there, tested RAID rebuild -- all looks good. Slow on an rpi but it worked.

Mounted md0 on /mnt/data; updated fstab accordingly. Again, all good.

Followed Dave Young's nginx guide to get things set up, but used the most recent OwnCloud (9.1.4). Had to chmod 0770 some permissions but was able to run the standard install wizard, pointed the data folder at /mnt/data, and let fly.

...but nothing is working. Still getting file integrity warnings, and cannot see anything on the /mnt/data. Followed the OwnCloud docs re: strong directory permissions, did a lot of chmod -R 0775 and chown'ing to www-data, and even tried hitting the occ DB update script directly -- nada, even after rebooting the pie.

sudo -u www-data ls -la /mnt/data

and

sudo -u www-data ls -la /var/www/owncloud

all return a list of files with rwxrwxr-x and cursory checks on the sub-folders looks like they're all owned by www-data.

I'm out of ideas -- thoughts?