Choosing a NAS solution where you can’t mount the storage media outside of the NAS is asking for trouble. I was worried I’d made the wrong choice when I found that mounting the ReadyNAS do ext3 drives is not trivial, mainly because they use a 16kb block size with their SPARC cpus.
A bit of routing around found various solutions, but the one which worked for me was as follows.
Fire up ubuntu vm (running on OS X for me and in my case 9.10 Karmic)
install lvm2 with a apt-get install lvm2
Download ext2fuse 0.5 (from here for example)
run vgscan to locate drives
vgchange -ay c to allow access to drive
ext2fuse /dev/c/c /mnt/lvm (where ext2fuse will have been downloaded)
drive can now be accessed on /mnt/lvm