Troubleshooting Backups

There are a few reasons the MySQL Cluster native backup tool may fail to make a backup. The following sections discuss a few common problems and how to solve them.

If a problem occurs while making a backup, it should always be reported in the cluster log. It is a good practice to monitor the cluster log for any such issues. The cluster log should give a general idea as to why the backup failed. It might be because someone manually aborted the backup by using the ABORT BACKUP command or be due to an uncontrollable cause, such as the three mentioned in the following sections.

In the unlikely event that the backup causes a node to fail, you can find more information in the node log and also in the trace file for the node that failed.

Disk Is Full

If you get a "disk is full" error, you need to ensure that the backup has enough space to complete. To solve this problem, you can either free up space or move BackupDataDir to some place that has more space.

Disk Is Too Slow

If the disk to which you are making a backup isn't fast enough, the backup might fail. A system of two different memory buffers is used when you make a backup. The first one is BackupDataBufferSize, which is used for buffering data before it is written to disk. The second one, which is important for this error, is BackupLogBufferSize. This is the buffer that is used to record data changes before writing to disk. If this buffer ever fills up due to the disk not being able to keep up with the number of changes occurring during the backup, the backup will fail. If that occurs, you can either attempt to increase this buffer or move the backup to be taken to a faster disk subsystem.

Not Enough Memory

As mentioned previously, some additional memory sections are allocated when performing a backup. If your system is too low on resources, this memory allocation can fail, which causes the cluster in MySQL Cluster to abort the backup process.

In order to fix this, you should either decrease the sizes of BackupDataBufferSize and BackupLogBufferSize or decrease another memory parameter in order to allow sufficient space for these to be allocated.