I have seen a few descriptions about using mdadm with lvm to create an easily expandable raid, such as this question, but I still think I'm missing something. Say that I create the raid using mdadm with 4 drives using raid5, then make an lvm volume(?) on top of that, then format that lvm volume with ext3. That all sounds good.
Then I want to add some more space, so I put another hard drive in. How do I add it? If I just add it to the lvm, then it is not part of the raid5 set. If I add it using "mdadm --grow", then after that is done, I still have to unmount and resize the ext3 filesystem.
I thought if I used lvm on top of mdadm it would be unnecessary to unmount and wait for the resize (which takes forever with a 5tb raid). Is that correct?
I have done this before without using lvm, using just "mdadm --grow", then I think resize2fs. But that took days, during which the drive had to be unmounted.