Vaulting; Power Loss To One Power Zone - EMC Symmetrix DMX-3 Product Manual

Data Integrity, Availability, and Protection

Vaulting

Powerdown operation
Powerup operation
Power loss to one
power zone
170 EMC Symmetrix DMX-3 Product Guide
As cache size, disk size, and power requirements have grown, the
time required to destage data has also increased. Vaulting is designed
to limit the time needed to power off the system if it needs to switch
to a battery supply. The vault image is fully redundant, with the
specified contents of global memory being saved twice to
independent disks.
When a DMX-3 is powered down, transitioned to offline, or when
environmental conditions trigger a vault situation, a vaulting
procedure is initiated. During powerdown or power loss, the part of
global memory being saved first reaches a consistent image (no more
writes). The disk directors then write the appropriate sections of
global memory to disk, saving two copies of the logical data. The
BBU modules maintain power to the system during the powerdown
process for up to five minutes.
During power up, the data is written back to global memory to
restore the system. When the Symmetrix system is powered on, the
startup program does the following:
Initializes the hardware and the environmental system.
Restores the global memory from the saved data while checking
the integrity of the data.
Performs clean-up, data structure integrity, and re-initialization of
needed global memory data structures.
At the end of startup program, the system resumes normal operation
when the BBU are recharged enough to support another vault. If any
condition is not safe, the system will not resume operation and will
call Customer Support for diagnosis and repair. In this state,
Customer Support will be able to communicate with the Symmetrix
system and find out the reason for not resuming normal operation.
The Symmetrix power subsystem two-zone design (A, B) ensures that
if there is an AC power loss to one of the zones, power from the
second power source will maintain power to the affected bay or bays,
provided that each system bay's or storage bay's two PDPs are
connected to two separate source PDUs at the customer's site. Upon
an AC power loss to a single power zone, the system will maintain
operation.