Building Disaster Recovery Serviceguard Solutions Using Metrocluster with Continuous Access XP P9000 for Linux B.12.00.00

NOTE: When a device group state is SVOL_PAIR on the
local site and EX_ENORMT (Raid Manager or node failure)
or EX_CMDIOE (disk I/O failure) on the remote site (this
means it is impossible for Metrocluster/Continuous Access
to determine if the data on the SVOL site is current),
Metrocluster/Continuous Access conservatively assumes that
the data on the SVOL site might by non-current and uses the
value of AUTO_NONCURDATA to determine whether the
package is allowed to automatically start up. If the value is
1, Metrocluster/Continuous Access allows the package to
startup; otherwise, the package will not be started.
Use the two scenarios below to help you determine the
correct environment settings for AUTO_NONCURDATA and
AUTO_FENCEDATA_SPLIT for your Metrocluster/Continuous
Access packages.
Scenario 1: With the package device group fence level
DATA, if setting AUTO_FENCEDATA_SPLIT=0, it is
guaranteed that the remote data site will never contain
non-current data (this assumes that the FORCEFLAG has not
been used to allow the package to start up if the Continuous
Access links or SVOL site are down). In this environment,
you can set AUTO_NONCURDATA=1 to make the package
automatically startup on the SVOL site when the PVOL site
fails, and it is guaranteed the package data is current. (If
setting AUTO_NONCURDATA=0, the package will not
automatically startup on the SVOL site.)
Scenario 2: When the package device group fence level is
set to NEVER or ASYNC, you are not guaranteed that the
remote (SVOL) data site still contains current data (The
application can continue to write data to the device group
on the PVOL site if the Continuous Access links or SVOL site
are down, and it is impossible for Metrocluster/Continuous
Access to determine whether the data on the SVOL site is
current.) In this environment, it is required to set
AUTO_NONCURDATA=0 if the intention is to ensure the
package application is running on current data. (If setting
AUTO_NONCURDATA=1, the package is started up on
SVOL site whether the data is current or not.)
AUTO_PSUEPSUS (Default = 0)
In asynchronous mode, when the primary site fails, either
due to Continuous Access link failure, or some other
hardware failure, and we fail over to the secondary site,
the PVOL will become PSUE and the SVOL will become
PSUS(SSWS). During this transition, horctakeover will
attempt to flush any data in the side file on the MCU to the
RCU. Data that does not make it to the RCU is stored on the
bit map of the MCU. When failing back to the primary site
any data that was in the MCU side file that is now stored
on the bit map is lost during resynchronization.
In synchronous mode with fence level NEVER, when the
Continuous Access link fails, the application continues
running and writing data to the PVOL. At this point the SVOL
contains non-current data. If there is another failure that
causes the package to fail over and start on the secondary
site, the PVOL becomes PSUE and the SVOL becomes
56 Package attributes for Metrocluster with Continuous Access XP P9000 for Linux