Ds400 Dual Controller Example Configurations; Ds400 Dual Controller Direct Attachment Single Path - IBM TotalStorage DS300 Best Practices Manual

8.3 DS400 dual controller example configurations

In this section we describe example configurations for the DS400 dual controller
model.
The DS400 dual controller model allows the configuration of a fully redundant
path from host systems to the logical drives, preventing single points of failure.
We recommend to use two HBAs in each attached server to take advantage of
this possibility.
Important: Controller failover within the DS400 occurs on an array basis, not
on a logical drive basis. If a host system accesses a logical drive, and loses its
path to the controller currently managing the array where the logical drive
resides, the whole array will be switched to the other controller. Other servers
also accessing logical drives within this array are also forced to switch to the
other controller.
It is best practice to assign logical drives within an individual array only to a
single host system. This eliminates the impact of such failovers to other host
systems.

8.3.1 DS400 dual controller direct attachment single path

In small environments it is possible to directly attach up to four host systems,
each with one host bus adapter, with a single path to the TotalStorage DS400. No
multipath driver is required. Most operating systems should have no problems
with this configuration.
There are some limitations which may result in a host system no longer being
able to access the logical drives of the TotalStorage DS400. This can happen
after a controller failover. In case of a controller failure, all arrays with the logical
drives will be failed over to the alternate controller. The hosts attached to the
original controller will not longer be able than to access the logical drives
because there exists only one path. This is simple configuration that leaves very
little room for failover and recovery and should be avoided.
Chapter 8. TotalStorage DS400 example configurations
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