Troubleshooting the error "Unable to write to disk due to reaching disk I/O limits"

Symptoms

You got an alert for a node:

Unable to write to disk due to reaching disk I/O limits

Solution

1. Verify the size of the shards does not exceed 25GB each.
2. Verify Slave shards spread across all nodes, multiple slave shards on a specific node can lead to multiple writes to one single node disk
3. Consider switching the persistence AOF policy from every write to every second, instead (Append Only File (AoF) one second)

References

Configure database persistence