I have a 500 and 64GB cache pool with 219GB free. So unless the pool is not working right, it is something else. I just looked through the VM log and the unraid log on the dashboard and I am seeing errors. I am new to unraid, but I would guess these errors are not good. This is not all of it, but they both seem to repeat the same errors so I just pasted part of it:
VM log:
2015-08-19 23:50:26.966+0000: starting up libvirt version: 1.2.15, qemu version: 2.3.0
Domain id=30 is tainted: high-privileges
Domain id=30 is tainted: host-cpu
char device redirected to /dev/pts/0 (label charserial0)
qemu: terminating on signal 15 from pid 15552
2015-08-20 00:45:58.223+0000: shutting down
2015-08-20 00:46:00.953+0000: starting up libvirt version: 1.2.15, qemu version: 2.3.0
Domain id=31 is tainted: high-privileges
Domain id=31 is tainted: host-cpu
char device redirected to /dev/pts/0 (label charserial0)
Dashboard log:
Aug 19 21:03:21 unraid kernel: blk_update_request: I/O error, dev loop0, sector 9251096
Aug 19 21:03:21 unraid kernel: BTRFS: bdev /dev/loop0 errs: wr 6454, rd 0, flush 0, corrupt 0, gen 0
Aug 19 21:03:22 unraid kernel: loop: Write error at byte offset 4736688128, length 4096.
Aug 19 21:03:22 unraid kernel: blk_update_request: I/O error, dev loop0, sector 9251344
Aug 19 21:03:22 unraid kernel: BTRFS: bdev /dev/loop0 errs: wr 6455, rd 0, flush 0, corrupt 0, gen 0
Aug 19 21:03:22 unraid kernel: loop: Write error at byte offset 4736696320, length 4096.
Aug 19 21:03:22 unraid kernel: blk_update_request: I/O error, dev loop0, sector 9251360
Aug 19 21:03:22 unraid kernel: BTRFS: bdev /dev/loop0 errs: wr 6456, rd 0, flush 0, corrupt 0, gen 0
Aug 19 21:03:22 unraid kernel: loop: Write error at byte offset 4736823296, length 4096.
Aug 19 21:03:22 unraid kernel: blk_update_request: I/O error, dev loop0, sector 9251608
Aug 19 21:03:22 unraid kernel: BTRFS: bdev /dev/loop0 errs: wr 6457, rd 0, flush 0, corrupt 0, gen 0
Aug 19 21:03:22 unraid kernel: loop: Write error at byte offset 4736950272, length 4096.
Aug 19 21:03:22 unraid kernel: blk_update_request: I/O error, dev loop0, sector 9251856
Aug 19 21:03:22 unraid kernel: BTRFS: bdev /dev/loop0 errs: wr 6458, rd 0, flush 0, corrupt 0, gen 0