On Gen8 servers, there is no 'Legacy boot mode' as the system firmware is BIOS and not UEFI.
How many logical drives were defined on the system when running CentOS 6.4?
Most OS's using MBR (BIOS) drive types have a 2TB limit for the boot drive and many have issues if /boot is above the 1024 cyluinder boundy. Create your RAID 5 with all of your drives, then create a couple of logical drives. Make the first logical drive somewhere between 500-900 GB for the OS, and use the remaining space for the second logical drive. Install /boot /swap and / on the first logical drive and depending on what the system will be doing make /var or equivilent the second logical drive.
As you can see on one of my systems, I have 24 900GB drives in a RAID 5 with spare. On this system, I actually have two seperate arrays, but the logical drives are what is presented to The OS
sudo dmidecode | grep ProLiant
Product Name: ProLiant DL380p Gen8
Family: ProLiant# df -h
Filesystem Size Used Avail Use% Mounted on /dev/sda2 822G 29G 752G 4% / tmpfs 16G 76K 16G 1% /dev/shm /dev/sdb1 17T 11T 6.0T 64% /data
# hpssacli ctrl all show config
Smart Array P420i in Slot 0 (Embedded) (sn: OU812)
Port Name: 1I
Port Name: 2I
Gen8 ServBP 25+2 at Port 1I, Box 1, OK
Gen8 ServBP 25+2 at Port 2I, Box 1, OK
array A (SAS, Unused Space: 0 MB)
logicaldrive 1 (838.3 GB, RAID 1, OK)
physicaldrive 1I:1:1 (port 1I:box 1:bay 1, SAS, 900.1 GB, OK)
physicaldrive 1I:1:2 (port 1I:box 1:bay 2, SAS, 900.1 GB, OK)
physicaldrive 2I:1:25 (port 2I:box 1:bay 25, SAS, 900.1 GB, OK, spare)
array B (SAS, Unused Space: 0 MB)
logicaldrive 2 (16.4 TB, RAID 6, OK)
physicaldrive 1I:1:3 (port 1I:box 1:bay 3, SAS, 900.1 GB, OK)
physicaldrive 1I:1:4 (port 1I:box 1:bay 4, SAS, 900.1 GB, OK)
physicaldrive 1I:1:5 (port 1I:box 1:bay 5, SAS, 900.1 GB, OK)
physicaldrive 1I:1:6 (port 1I:box 1:bay 6, SAS, 900.1 GB, OK)
physicaldrive 1I:1:7 (port 1I:box 1:bay 7, SAS, 900.1 GB, OK)
physicaldrive 1I:1:8 (port 1I:box 1:bay 8, SAS, 900.1 GB, OK)
physicaldrive 1I:1:9 (port 1I:box 1:bay 9, SAS, 900.1 GB, OK)
physicaldrive 1I:1:10 (port 1I:box 1:bay 10, SAS, 900.1 GB, OK)
physicaldrive 1I:1:11 (port 1I:box 1:bay 11, SAS, 900.1 GB, OK)
physicaldrive 1I:1:12 (port 1I:box 1:bay 12, SAS, 900.1 GB, OK)
physicaldrive 1I:1:13 (port 1I:box 1:bay 13, SAS, 900.1 GB, OK)
physicaldrive 2I:1:14 (port 2I:box 1:bay 14, SAS, 900.1 GB, OK)
physicaldrive 2I:1:15 (port 2I:box 1:bay 15, SAS, 900.1 GB, OK)
physicaldrive 2I:1:16 (port 2I:box 1:bay 16, SAS, 900.1 GB, OK)
physicaldrive 2I:1:17 (port 2I:box 1:bay 17, SAS, 900.1 GB, OK)
physicaldrive 2I:1:18 (port 2I:box 1:bay 18, SAS, 900.1 GB, OK)
physicaldrive 2I:1:19 (port 2I:box 1:bay 19, SAS, 900.1 GB, OK)
physicaldrive 2I:1:20 (port 2I:box 1:bay 20, SAS, 900.1 GB, OK)
physicaldrive 2I:1:21 (port 2I:box 1:bay 21, SAS, 900.1 GB, OK)
physicaldrive 2I:1:22 (port 2I:box 1:bay 22, SAS, 900.1 GB, OK)
physicaldrive 2I:1:23 (port 2I:box 1:bay 23, SAS, 900.1 GB, OK)
physicaldrive 2I:1:24 (port 2I:box 1:bay 24, SAS, 900.1 GB, OK)
physicaldrive 2I:1:25 (port 2I:box 1:bay 25, SAS, 900.1 GB, OK, spare)