Specifications

Escala Tower PL & S, E, T System Hardware
Chapter 3: External Storage and SAN Subsystems 52/116
9es3s1c3.doc
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02/12/2003
ATF is easy to manage. The initial configuration is fully automatic. ATF retrieves itself the SP pairs.
Failover is automatic, based in the IO errors returned by the host bus adapters in case of unreachability
of LUNs. The trespass command enables to force IO rerouting, for example for maintenance
operations. The restoration of initial IO routing after repair is also controlled by the administrator. All
ATF path management operations are logged in each server's errlog (for AIX), enabling an easy
tracking. Navisphere tools (for AIX or for NT) enable to check the current SP attached for each LUNs,
to control which path is currently used, and what is the default configuration.
Furthermore, ATF is integrated with HA-CMP to enable intelligent failover: failure of a single path is
managed by ATF, whereas dual path failure leads to node takeover.
ATF fully uses the dual active architecture of the DAS subsystems. During normal operations, the two
paths to the disk subsystem are active, and are used by the server's I/O traffic. The I/O workload can
be balanced between the two storage processors, to deliver optimal performances. This load balancing
is managed by the storage administrators, at the initial DAS configurations. There is a single active
path for each LUN, through the SP processor where it is bound be default. Thus, administrators must
balance the LUNs across both storage processors, taking into account the expected IO load for each
LUN, to optimize the performances. The load balancing is automatically tuned based on the effective
IO load, but it is possible to change the LUN to SP bindings, transparently for the applications.
Administrators can modify the LUN balancing to optimize the performances, without stopping the
applications.
ATF operates with all DAS models (series 1000, 2000, 3000, 4000, and 5000), but not with the DAE
5000, which is a JBOD and not a RAID subsystem. Any type of Escala server and AIX versions are
supported. Any type of connection can be used (SCSI, fibre channel point-to-point, loop, fabrics, …).
ATF is compatible with LUN access control features deployed in SAN environments (such as zoning,
LUN masking with AIX SAN Manager or Access Logix), as long as the SAN administrators take care
to allow LUN access through two distinct paths.
ATF Version 2.1 requires iFOR/LS license keys. ATF Version 2.2 is delivered without license keys.
The migration ATF to PowerPath is available only for DAS4500, DAS4700 and DAS5300
4.6. PowerPath Full and PowerPath Base
PowerPath software is a server-resident, performance and information availability enhancing software
solution. PowerPath also supports high availability cluster environments.
•
PowerPath Full integrates multiple path I/O capabilities, automatic load balancing, and path
failover functions into one comprehensive package for use on platforms connected to Symmetrix
or DAS storage sub-systems.
•
PowerPath Base integrates only path failover functions into one comprehensive package for use on
platforms connected to Symmetrix or DAS storage sub-systems.
The PowerPath software resides on the open server platforms and supports SCSI (Symmetrix only),
and Fibre Channel for both switched fabric and arbitrated loop environments.