PE = "physical" extent. You have two "physical" disks for each extent.
LE = "logical" extent. Essentially this is "usable" space. So 2 GB mirrored = 1 GB "usable".
By the way it sounds as if you're discussing HP-UX. If so you should know there are other forums with higher visibility than this one for HP-UX.
HP has forums at itrc.hp.com.
Also there is a mailing list called Dutchworks. Details for it:
To subscribe/unsubscribe to this list, contact
Archives: ftp.dutchworks.nl:/pub/digests/hpux-admin (FTP, browse only)
(Web, browse & search)
For whatever reason the folks that run Linuxquestions.org don't seem to think HP-UX worthy of its own forum so there's no reason to use them for it.