Function Of Auto-Logical Drive Transfer Feature - IBM System Storage DS3500 Introduction And Implementation Manual

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RDAC implementation
RDAC is implemented between the HBA driver and the operating system disk driver,
operating as a low-level filter driver. It has the following advantages:
It is much more transparent to the OS and applications.
I/O controls at the HBA driver level are not as tightly coupled to the OS as those at the disk
driver level. Consequently, it is easier to implement I/O control functionality in the
MPP-based RDAC driver for routing functions.
Because the driver is positioned at the HBA level (see Figure 3-26), it has access to the SCSI
command and sense data interface of the HBA driver and therefore can make more informed
decisions about what to do in the case of path failures.
Figure 3-26 Linux RDAC/MPP driver
Note: In Linux, RDAC cannot be installed with the Installation Wizard. If you need RDAC,
you have to download and install it separately.
DMM for Linux
At the current time DMMP for Linux is only supported with the SLES 11 release of Linux.
There is currently no Redhat version of this driver supported today. With the SLES 11 the
following requirements must be adhered to for the driver to function:
OS version: SLES11.0 with the following patch installed
patch installed: lsi-scsi_dh_rdac-kmp-default-01.00_2.6.27.19_5-1
kernel upgraded to 2.6.31.5-0.16-default
DMM version: device-mapper-1.02.27-8.6
For detailed instructions on how to implement and use DMM with SLES 11 see Chapter 20,
"SuSE Linux configuration guide" on page 603.

3.6.10 Function of Auto-Logical Drive Transfer feature

In a DS3500 Storage System equipped with two controllers, you can provide redundant I/O
paths with the host systems. There are two separate components that provide this
redundancy: a multipathing driver and Auto-Logical Drive Transfer (ADT).
ADT for logical drive-level failover
ADT is a built-in feature of controller firmware that allows logical drive-level failover rather than
controller-level failover (as is the case with RDAC).
Note: ADT is not a failover driver. ADT provides storage systems with the flexibility to work
with certain third-party failover software.
ADT-disabled failover:
The multi-path software will send a SCSI Mode Select command to cause a change in
volume ownership before using the alternate path. All logical drives on the preferred
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IBM System Storage DS3500: Introduction and Implementation Guide
Draft Document for Review March 28, 2011 12:24 pm