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Chapter 2. Components 35
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.
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Server 0 device
adapter
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Rear storage
enclosure N max=6
Rear storage
enclosure 2
Server 1 device
adapter
FC switch
8 or 16 DDMs per
enclosure
2Gbs FC-AL link
4 FC-AL Ports
Rear
enclosures
Front
enclosures
Rear storage
enclosure 1
Front storage
enclosure 1
Front storage
enclosure 2
Front storage
enclosure N max=6