LVM on top RAID: Disadvantages?

Hi All,
I have use RAID on my slackware box for a long time (about 10 years) but i never use LVM because I don't see advantages in it. I try it several times but without find real utility.

At the moment I have an array of six 6TB Red drive in RAID6 formated in JFS and it work fine for many years (the array have almost 5 year). But I want to make snapshot so i'm sure that when i begin a backup all the data are consistent.

This is plan:

• Make two partion on each drive
  1. The first, 99% of the disk, for data. This is give me the security in the unfortunate hypothesis that it must change drive in case of breakage. Mdadm does not accept drive smaller than the original one. For this reason at the moment I have left 50 MB at the end of the 6TB drive. But I think that's not enough.
  2. The second, 1% of the disk, i will enlarge the unused space from the current 50 MB up to 1% of the disk. In this way I can create a second partion to use for snapshot.
• Create two mdadm raid. One for the real data and one for store the changes in the snapshot.
• Create a VG of the two md-device in linear mode
• Create a LV of the size of the data raid
• Mount/use the LV created

in case of backup i will create a snaphot using the free space.

Questions:

1. Is there any downside in what I want to do?
2. Now I use JFS... is a good FS o i must migrate to an other ( I am evaluating XFS )?
3. I'm want to use RAID/LVM only for data not for boot. I need some special configuration?
4. any suggestion?

Best regards,
Razziatore