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Chapter 2. Components 33
spare. So at least two spares are created per loop, which will serve up to four enclosures,
depending on the disk intermix.
2.5 Server enclosure RAID controller card
The RAID controller cards are the heart and soul of the system. Each card is the equivalent of
a cluster node in an ESS. IBM has leveraged its extensive development of the ESS host
adapter and device adapter function to create a total repackaging. It actually uses DS8000
host adapter and device adapter logic, which allows almost complete commonality of function
and code between the two series (DS6000 and DS8000).
2.5.1 Technical details
From a technical point of view the controller card is powered by an IBM PowerPC 750GX
1GHz processor. The controllers do not have an internal hard drive, but instead contain a
compact flash memory card to act as a boot device and to store microcode and log data.
Each controller contains 2 GB of server memory, giving the DS6800 a total of 4 GB. A certain
portion of that memory is reserved as persistent memory or non-volatile storage (NVS). The
NVS memory is not located on a separate battery protected card like you would find in an
ESS 800. It instead shares the same memory DIMMs with all the other functions. To protect
the NVS memory area, a battery backup unit preserves the entire cache memory in the event
of an unexpected power failure. If the DS6800 were to power off with un-destaged writes in
NVS, then after reboot, the controller would read this reserved area and destage the writes.
For more details on the batteries themselves and controller failover see Chapter 3, “RAS” on
page 45.
Figure 2-11 DS6800 controller card
2.5.2 Device adapter ports
The DS6800 controller card is pictured in Figure 2-11. On the left-hand side, surrounded by
light and dark blue boxes (for readers seeing this in black and white, they appear to be light
and dark grey), are the disk expansion and disk control ports respectively. These ports are
used to attach up to a total of seven expansion enclosures to the server enclosure.
The device adapter ports provided in each controller are effectively the chipset from one
DS8000 device adapter. This provides remarkable performance thanks to a new high
function/high performance ASIC. To ensure maximum data integrity it supports metadata
creation and checking. Each controller provides four 2 Gb/sec device adapter ports, giving
the machine a total of 8 device adapter ports. These ports must be short wave and use
multimode cables with LC connectors.
The disks in the server enclosure are on the first disk loop (loop 0). When you attach the first
expansion enclosure you attach it to the
DISK CONTRL ports to start the second disk loop
(loop 1). The
DISK EXP ports are used to attach the second expansion enclosure. It joins the
same switched loop as the disks in the server enclosure (loop 0). The two loops are depicted