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6 DS6000 Series: Concepts and Architecture
1.2.1 Hardware overview
The DS6000 series consists of the DS6800, Model 1750-511, which has dual Fibre Channel
RAID controllers with up to 16 disk drives in the enclosure (see Figure 1-1 on page 4).
Capacity can be increased by adding up to 7 DS6000 expansion enclosures, Model
1750-EX1, each with up to 16 disk drives, as shown Figure 1-3.
Figure 1-3 DS6800 with five DS6000 expansion enclosures in a rack
DS6800 controller enclosure (Model 1750-511)
IBM TotalStorage systems are based on a server architecture. At the core of the DS6800
controller unit are two active/active RAID controllers based on IBM’s industry leading
PowerPC® architecture. By employing a server architecture with standard hardware
components, IBM’s storage division can always take advantage of the best of breed
components developed by other IBM divisions. The customer gets the benefit of a very cost
efficient and high performing storage system.
The processors
The DS6800 utilizes two 64-bit PowerPC 750GX 1 GHz processors for the storage server and
the host adapters, respectively, and another PowerPC 750FX 500 MHz processor for the
device adapter on each controller card. The DS6800 is equipped with 2 GB memory in each
controller card, adding up to 4 GB. Some part of the memory is used for the operating system
and another part in each controller card acts as nonvolatile storage (NVS), but most of the
memory is used as cache. This design to use processor memory makes cache accesses very
fast.
When data is written to the DS6800, it is placed in cache and a copy of the write data is also
copied to the NVS of the other controller card, so there are always two copies of write data
until the updates have been destaged to the disks. On zSeries, this mirroring of write data can
be disabled by application programs, for example, when writing temporary data (Cache Fast
Write). The NVS is battery backed up and the battery can keep the data for at least 72 hours
if power is lost.
The DS6000 series controller’s Licensed Internal Code (LIC) is based on the DS8000 series
software, a greatly enhanced extension of the ESS software. Since 97% of the functional
code of the DS6000 is identical to the DS8000 series, the DS6000 has a very good base to
be a stable system.