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14.1.2 Configuring MySQL for DRBD »
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14.1.1.7. Additional DRBD Configuration Options

Additional options you may want to configure:

  • protocol — specifies the level of consistency to be used when information is written to the block device. The option is similar in principle to the innodb_flush_log_at_trx_commit option within MySQL. Three levels are supported:

    • A — data is considered written when the information reaches the TCP send buffer and the local physical disk. There is no guarantee that the data has been written to the remote server or the remote physical disk.

    • B — data is considered written when the data has reached the local disk and the remote node's network buffer. The data has reached the remote server, but there is no guarantee it has reached the remote server's physical disk.

    • C — data is considered written when the data has reached the local disk and the remote node's physical disk.

    The preferred and recommended protocol is C, as it is the only protocol which ensures the consistency of the local and remote physical storage.

  • size — if you do not want to use the entire partition space with your DRBD block device then you can specify the size of the DRBD device to be created. The size specification can include a quantifier. For example, to set the maximum size of the DRBD partition to 1GB you would use: 

    size 1G;

With the configuration file suitably configured and ready to use, you now need to populate the lower-level device with the metadata information, and then start the DRBD service.