IBM DS8000 manual Expansion, Arrays and spares

Rear enclosures

Rear storage enclosure N max=6

Rear storage enclosure 2

Rear storage enclosure 1

15

0

15

0

15

0

FC switch

8 or 16 DDMs per

enclosure

2Gbs FC-AL link

4 FC-AL Ports

Server 0 device adapter

	Front storage
	enclosure 1
Front	Front storage
enclosures
	enclosure 2
	Front storage
	enclosure N max=6

0

15

0

15

0

15

Server 1 device adapter

Figure 2-13 DS8000 switched disk expansion

Expansion

Expansion enclosures are added in pairs and disks are added in groups of 16. On the ESS Model 800, the term 8-pack was used to describe an enclosure with eight disks in it. For the DS8000, we use the term 16-pack, though this term really describes the 16 DDMs found in one disk enclosure. It takes two orders of 16 DDMs to fully populate a disk enclosure pair (front and rear).

To provide an example, if a machine had six disk enclosures total, it would have three at the front and three at the rear. If all the enclosures were fully populated with disks, and an additional order of 16 DDMs was purchased, then two new disk enclosures would be added, one at the front and one at the rear. The switched networks do not need to be broken to add these enclosures. They are simply added to the end of the loop. Half of the 16 DDMs would go in the front enclosure and half would go in the rear enclosure. If an additional 16 DDMs were ordered later, they would be used to completely fill that pair of disk enclosures.

Arrays and spares

Array sites containing eight DDMs are created as DDMs are installed. During configuration, discussed in Chapter 10, “The DS Storage Manager - logical configuration” on page 189, the user will have the choice of creating a RAID-5 or RAID-10 array by choosing one array site. The first four array sites created on a DA pair each contribute one DDM to be a spare. So at least four spares are created per DA pair, depending on the disk intermix.

Chapter 2. Components 35