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- block: I/O waits until the buffer is free (until it can be queued to the buffer). This is the default when no congestion policy is set.
- disconnect: Disconnect the replication connection and enter the StandAlone state.
- pull-ahead: Enter delayed replication mode. If this is the case, the replication connection is maintained, but replication is stopped and local I/O is written on out-of-sync, and finally resynchronization is performed for the out-of-sync that was recorded when the congestion was released.
2.3.2. Buffer Size Tuning
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- It assumes DRBD asynchronous replication and Ahead mode (delayed replication) configuration.
- Ensure that only the I/O measurements of the interval during which the replication connection is maintained can be measured. The I/O measurements for the replication disconnect interval are not considered.
- The number of times DRBD enters Ahead mode (the number of congestion entries) is collected by the following method.
- Output count of "Congestion-fill threshold reached" on drbd log
- Check the number of Ahead entries through the drbdsetup events2 command
- Resizes the buffer based on the number of congestion entries collected. If the frequency of congestion is frequent, the size of the buffer should be increased.
- If the congestion interval does not decrease even though the buffer has been added, consider compression.
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