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Configuring your Environment for Software RAID
Configuring the Package Control Script and RAID Configuration File
Chapter 3 79
more time elapses than what is specified for RPO_TARGET, the
package is prevented from starting on the remote node (assuming
that the node still has access only to its own half of the mirror).
By default, RPO_TARGET is set to 0. Leave it at 0 to ensure the
package does not start on an adoptive node with a mirror half that is
not current. This ensures the highest degree of data currency.
If RPO_TARGET is not set to 0, the value of RAID_MONITOR_INTERVAL
should be less than the value of RPO_TARGET.
(RAID_MONITOR_INTERVAL should also be less than the value of the
Link_Down_Timeout parameter so that disk access failure can be
recognized early enough in certain failure scenarios.)
IMPORTANT A very low value of RAID_MONITOR_INTERVAL (less than 5 seconds)
has some impact on system performance because of the high
frequency of polling.
You can also set RPO_TARGET to the special value -1 or to any positive
integer. Setting RPO_TARGET to -1 causes the RAID system to ignore
any time-window checks on the disk set. This allows the package to
start with a mirror half that is not current.
Setting the RPO_TARGET to any positive integer, means that the
package will start with a mirror half that is not current by any
number of seconds less than that value. For example, an RPO_TARGET
of 45 means that the package will start only if the mirror is up to
date, or out of date by less than 45 seconds.
Because some timers are affected by polling, the value of this
parameter can vary by approximately 2 seconds.
This also requires that the minimum value of this parameter is 2
seconds if a small value is necessary. Change the value of
RPO_TARGET, if necessary, after considering the cases discussed
below.
Cases to Consider when Setting RPO_TARGET
RPO_TARGET allows for certain failure conditions when data is not
synchronized between the two sites.