User`s guide

Chapter 2. IBM TotalStorage Enterprise Storage Server configuration 109
The unformatted size of the disk groups is 254.8 GB. This is equivalent to seven
disks of a capacity of 36.4 GB each. In the ESS, we have two spare disks per
SSA loop. In our ESS we have sixteen disk groups, four per device adapter pair
and two per SSA loop. This is the reason why every one of our disk groups
contains one spare disk. This makes up the total unformatted capacity of 254.8
GB per disk group.
Defining two disk groups for RAID 5
We are going to define the disk groups connected to the A loop of the device
adapter pair 4 as RAID array. To do this, we select the first disk group we want to
configure and select Raid Array from the Storage Type pull-down menu.
The storage type, as shown in Figure 2-39, can be RAID Array, or non-RAID.
Non-RAID means the disks are going to be configured as “just a bunch of disks”
(JBOD).
Figure 2-39 Open systems storage types
Doing this also changes the Track Format to Fixed Block (FB) in the Track
Format pull-down menu. After doing this, we select the second disk group in the
other cluster, and also select Raid Array.
The Modification column of the panel, as shown in Figure 2-40, shows that we
have made changes (Defined), and the Capacity column shows that our disk
groups are still unformatted. In this case, formatted to the ESS means it is not
formatted as either a RAID array or as non-RAID.
Note: The disk groups should not be mistaken for the eight packs, which are
the physical disk packages, that are installed in the ESS. The disk groups are
logical groups that consist of disks from two eight packs, four disks from each
of the two. This is the reason why it is only possible to upgrade the ESS in
steps of two eight packs.