I have been doing some benchmarks reading with dd from both the LVM device and the PV device and I got some unexpected results:
$ sync ; echo 3 > /proc/sys/vm/drop_caches; dd bs=1M count=1024 if=/dev/sdc of=/dev/null
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 2.06466 s, 520 MB/s
[~]
$ sync ; echo 3 > /proc/sys/vm/drop_caches; dd bs=1M count=1024 if=/dev/mapper/vg-data of=/dev/null
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 9.07621 s, 118 MB/s
[~]
The difference is consistent on multiple runs, why is there such a difference and what of the transfer rate should be expected from applications reading from the corresponding FS?