Just to clarify further on the question of defragging a RAID Group... the only time you need to defrag is if you have more "free space" than "contiguous free space". If they show the same value you are fine. I the free space is larger than the contiguous free space than you will need to defrag if you need more than the available contiguous space for your next LUN.  As a best practice in our shop, we always check when we remove a LUN and trigger a defrag immediately if one is required. That way we don't need to wait if we need to do an emergency allocation later.  As already explained, you wouldn't have to worry about it in your described case because the defrag would not gain you anything. But I'll describe a situation in which it could.  If you have a 5 drive RAID Group of 146GB drives you will get roughly 533GB usable if you build RAID 5 LUNs. So we will bind a 5 x 100GB LUNs on this RAID group - LUNs 1,2,3,4 & 5 in order. Later that week the host that LUN 2 was assigned to crashes and needs to be rebuilt from scratch. Before you assign the LUN to the new server the Server Admin tells you that he really needs a single 130GB LUN instead of 100GB. You destroy LUN 2. This leaves you with 133GB free on the RAID Group, but you can still only build a 100GB LUN (because the empty space isn't contiguous). You run a defrag on the RAID Group and when it completes you are able to bind your new LUN2 with 130GB as requested and allocate it to the server.  A picture would probably make it easier, but even if I could draw here I'm no artist. Hopefully the words help enough :-)
Clariion CX3-80 Navispere 6  I have question:  It was cretaed Raid group X [RAID 5;FC]. No private Luns inside RAID group. Overall thee is 6 disks of 66.64GB. There is two LUN overthere:  1st:  User Capacity: 70GB Raw Capacity: 87.5GB  2nd  User Capacity: 64.55GB Raw Capacity: 80.694GB  Question 1: RAID 5 will give 248.25GB total usable space. That is not the case. Why? Even if I  bind new LUN there is no free space for it. Where are around 80 GB?  Question 2: If I unbind one of the LUN (let say LUN 1st), the RAID group will free the DISK space inside RAID group?  Or I have to defragment RAID group? 
Cx3-80 Newbie question : Raid 5