When a LV shows as inactive, I'ld try something like:
Side note: something's weird ... Either you setup your RAID from your bios, and then that's a hardware raid, your system only sees a virtual device (/dev/sdX). Even if you do not have some dedicated card dealing with this: your motherboard can play that role.
Or you have a software raid, ...
Let fdisk do it's job on the external drive (if you need to create one or more partitions). Use the default partition type (don't worry about it).
Then use mkfs.ext4 and create an ext4 file system.
Use gparted and let it create partition(s) and file system(s).
Now I know how to put it, Ben:
Looking at your intention:
want to change a partition to Ext3 or Ext4
and looking at your choices:
19-31, as fdisk lists: no type Ext!
This is a contradiction!
Partitions have a part-of-disk fdisk and a block-with-fs mkfs nature.
Type as hints: true!
systemd takes them serious. After I had added some more ...
Yes, resize2fs moves data as needed (at least on ext4). That means that lvreduce -r (the -r is critical) is safe as well, because it first calls resize2fs via fsadm. Note that ext4 can shrink only in offline mode (when unmounted); trying to do it while mounted should just error out.
Of course, "safe" is only if there are no bugs, power isn't cut in the ...