How to read binary contents of free disk space in CentOS
The easiest is probably indeed with dd.
dd if=/dev/VG_NAME/LV_NAME of=/tmp/partition.data skip=500M bs=1M count=5
will skip the first 500 Megabytes of raw data from the block device and then copy out count=5 * 1 Megabyte of raw data to the filename specified with of.
Read and repeat with different offsets.