Designing Disaster Tolerant High Availability Clusters, 10th Edition, March 2003 (B7660-90013)

Building a Metropolitan Cluster Using MetroCluster/CA
Preparing an MC/ServiceGuard Cluster for MetroCluster /CA
Chapter 3 91
there is enough room in the side file. Before continuing to write, the
primary XP will wait until there is enough room in the side file, and will
keep trying until it reaches its side file timeout value, which is
configured through the SVP. If timeout has been reached, then the
primary XP disk array will begin tracking data on its bitmap which will
be copied over to the secondary volume during resync.
The side file operation is shown in Figure 3-9.
Figure 3-9 XP Series Disk Array Side File
NOTE The side file must be configured using the XP Service Processor (SVP).
Refer to the XP Series documentation for details.
In case all the CA links fail, the remaining data in the side file that has
not been copied over to the SVOL will be tracked in the bit map. The
application continues to modify the data on the PVOL, which will also
betracked in the bit map. The SVOL only contains a copy of the data up
to the point the failure of the CA links. If an additional failure, such as a
system failure before the CA link is fixed, causes the application to fail
over to the SVOL side, the application will have to deal with non-current
data.
CA Link Timeout
In asynchronous mode, when there is an CA link failure, both the PVOL
and SVOL sides change to a PSUE state. When the SVOL side detects
missing data blocks from the PVOL side, it will wait for those data blocks
from the PVOL side until it has reached the configured CA link timeout
value (set in the SVP). Once this timeout value has been reached, then
the SVOL side will change to a PSUE state. The default CA link timeout
value is 5 minutes (300 seconds).
Side File Area
High Water Mark
(30% of cache)
Writing responses
are delayed
Side File
Writing waits until the
quantity of data is under
threshold unless timeout has
been reached
Cache