the data is written to volatile memory on one controller and persistent memory on the other controller. The DS6800 then reports to the host that the write is complete before it has actually been written to disk. This provides much faster write performance. Persistent memory is also called NVS or
SAN fabric
host adapter |
chipset |
Power PC |
chipset |
device adapter |
chipset |
Controller card 0
Volatile memory
Persistent memory
Controller card 1
Volatile memory
Persistent memory
host adapter |
chipset |
Power PC |
chipset |
device adapter |
chipset |
Server enclosure
20 port fibre channel switch | 20 port fibre channel switch |
20 port fibre channel switch | 20 port fibre channel switch |
First expansion enclosure (if present)
Figure 2-4 DS6000 architecture
When a host performs a read I/O, the controllers fetch the data from the disk arrays via the high performance switched disk architecture. The data is then cached in volatile memory in case it is required again. The controllers attempt to anticipate future reads by an algorithm known as SARC (sequential prefetching in adaptive replacement cache). Data is held in cache as long as possible using this smart algorithm. If a cache hit occurs where requested data is already in cache, then the host does not have to wait for it to be read from the disks.
26DS6000 Series: Concepts and Architecture
