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192 DS8000 Series: Concepts and Architecture
One set of host definitions may be used for multiple storage images, storage units, and
storage complexes.
DDM
A Disk Drive Module (DDM) is a field replaceable unit that consists of a single disk drive and
its associated packaging. DDMs are ordered in a group of 16 called a drive set. A drive set is
installed across two disk enclosures, 8 DDMs in the front disk enclosure and 8 DDMs in the
rear disk enclosure. When ordering disk enclosures they come in pairs, each able to hold 16
drives. If any disk enclosure is not full of DDMs, then the empty slots must be filled with
dummy carriers called
disk enclosure fillers. Disk enclosure fillers can be ordered in groups of
16 per order.
Array sites
An array site is a predetermined grouping of eight individual DDMs of the same speed and
capacity. Four disks from a rear disk enclosure and four disks from a front disk enclosure
make up the array site.
Arrays
Arrays consist of DDMs from an array site, used to construct one RAID array. An array is
given either a RAID-5 or RAID-10 format.
Ranks
One array forms one CKD or Fixed Block (FB) rank. When the rank is configured, either CKD
or FB characteristics are taken on at this point. Presently only one array can reside in a rank,
but in the future one or more arrays will be able to reside in one rank.
Extent pools
An extent pool consists of one or several ranks. Ranks in the same extent pool must be of the
same data format (CKD or FB). Each extent pool is associated with server 0 or server 1.
Although it is possible to create extent pools with ranks of different drive capacities, speeds,
and RAID types, we recommend you create them to consist of the same RAID type, speed,
and capacity. Also, we recommend that you configure only half of the total number of ranks to
reside in one pool (server 0) and the other half in the other pool (server 1). Extent pools
contain one or more ranks divided into fixed-size extents as follows:
CKD extents are equal to a 3390 Mod1
FB extents are 1GB
The storage in an extent pool (the extents from each rank in the extent pool) is used to create
logical volumes. We recommend that you create one extent pool out of only one rank to start
with, unless the size required for a Fixed Block logical volume (LUN) is larger than the
combined free extents residing in one single rank.
Note: The ranks have no pre-determined relation to an LSS.