IBM DS8000 manual Array sites, Arrays, Ranks, Extent pools

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.

Note: The ranks have no pre-determined relation to an LSS.

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.

192DS8000 Series: Concepts and Architecture