IBM DS6000 Series Server enclosure RAID controller card, Technical details, Device adapter ports

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

Chapter 2. Components 33