LUN Expansion on XP24000

[SRCPLee]

I am configuring LUNs for D2D backups on our XP24000 array and need to know if my LUN expansion methods are proper.

I have two internal boxes (3&5) with 15 unused parity groups (RAID5 7D+1P) and two internal boxes (11&13) with two unused parity groups (RAID5 7D+1P) in each box. I have created a single LDEV on each PG utilizing all free space (2872GB) in the PG. Each LDEV is drawn from the CU pool corresponding to the box number, i.e. box # 3 PG 1 = 00:03:00 and box 5 PG 1 = 00:05:00.

The backup administrator needs 80 - 90TB for D2D backups. I plan to create eight LUNs >11TB to present to the two backup servers. To do that I will need to concatenate four LDEVs. I have  created two expanded LUNs by adding one LDEV from each box, thinking this would spread the LUN across all four boxes for best performance/redundancy. This used up both PGs in the small boxes (11&13) and leaves 13 PGs in the two large boxes (3&5) for the other six LUNs.

How should I align the LDEVS for the final six LUNs ? Two from one box (3) with two from the other box (5) or one from each box plus another one from each box ?

00:03:02 + 00:03:03 + 00:05:02 + 00:05:03

or

00:03:02 + 00:05:02 + 00:03:03 + 00:05:03

Or does it make a difference ?