The cluster.routing.allocation.disk.watermark.enable_for_single_data_node setting in Elasticsearch controls whether disk-based shard allocation should be enabled for clusters with only a single data node.
Description
- Default value:
false - Possible values:
trueorfalse - Recommendation: Keep the default value unless you have specific requirements for single-node clusters.
This setting determines if Elasticsearch should apply disk watermark-based allocation decisions in clusters with only one data node. By default, it's disabled to prevent unnecessary shard movements in single-node setups.
Example
To enable disk watermark allocation for single data node clusters:
PUT _cluster/settings
{
"persistent": {
"cluster.routing.allocation.disk.watermark.enable_for_single_data_node": true
}
}
Enabling this setting might be useful in development environments or when testing disk-based allocation behaviors on a single-node cluster. However, it's generally not recommended for production single-node clusters.
Common Issues
- Enabling this setting unnecessarily can lead to frequent shard relocations in single-node clusters, potentially impacting performance.
- Misunderstanding the purpose of this setting and enabling it in multi-node clusters (where it has no effect) can lead to confusion.
Do's and Don'ts
- Do keep this setting disabled for most single-node production clusters.
- Do enable it if you need to test or simulate disk-based allocation behaviors on a single-node setup.
- Don't enable this setting thinking it will improve disk management in multi-node clusters; it only affects single-node setups.
- Don't ignore disk space issues on single-node clusters just because this setting is disabled; monitor disk usage regularly.
Frequently Asked Questions
Q: Why is this setting disabled by default?
A: It's disabled to prevent unnecessary shard movements in single-node clusters, where disk-based allocation decisions are typically not beneficial.
Q: Does this setting affect multi-node clusters?
A: No, this setting only impacts clusters with a single data node. In multi-node clusters, disk-based allocation is always active regardless of this setting.
Q: When should I consider enabling this setting?
A: You might enable it in development or testing environments to simulate disk-based allocation behaviors on a single node, or in specific single-node production scenarios where you want to enforce disk watermark rules.
Q: Can enabling this setting help prevent disk full scenarios in single-node clusters?
A: While it can help by relocating shards based on disk usage, it's not a substitute for proper disk management and monitoring in single-node setups.
Q: How does this setting interact with other disk allocation settings?
A: When enabled, it allows other disk allocation settings (like low and high watermarks) to take effect on single-node clusters, which they wouldn't otherwise.
