Splunk SmartStore Cache Filling Up Disk.

Applicability

Splunk Enterprise 9.0.3

Description

Splunk SmartStore is a cache manager that effectively manages data placement between remote object stores and the local cache, providing a highly scalable and cost-effective data storage solution. However, operational challenges may arise when the local cache begins to fill up, potentially leading to network operation timeouts and affecting data eviction processes.

SmartStore Cache was filling up the local disk, causing subsequent issues with data eviction. The system logs indicated that some replication operations were timing out on the indexers, preventing the proper eviction of data buckets. Consequently, the minimum free disk space limit was reached, causing search schedulers to halt.

Investigation

Upon investigation, it was found that there was a well-configured SmartStore setup on the Google Cloud Platform. The SmartStore cache size and eviction parameters were appropriately set.

An in-depth analysis of system logs and configuration files revealed multiple factors contributing to the problem:

1. Space Availability Issues: A series of logs indicated the SmartStore cache was consistently running out of free disk space. Despite having eviction policies set, the system could not evict data fast enough to create the needed free space for new data.

    WARN CacheManager [1232359 cachemanagerDownloadExecutorWorker-7101] - Unable to evict enough data. Evicted size=0 instead of size=126504226816
   

2. Network Timeout: Some replication operations were timing out. This was initially indicated by the logs reporting failed operations due to timeouts.

In light of these findings, it was evident that network operation timeouts were affecting the proper functioning of the SmartStore cache, leading to inadequate eviction of data and eventual filling up of the local disk.

Troubleshooting steps:

1. Inspection of logs: Log analysis helped identify the key issues—local disk space exhaustion, network operation timeout, and eviction issues.

2. Review of Configuration Files: The indexes.conf and server.conf files were reviewed to understand the current setup and configurations.

Resolution

To address the timeout issues, increase the timeout limits from 60 seconds to 300 seconds for the following parameters in the server.conf file under [clustering] stanza in the indexers and in the cluster manager (CM), to set custom configurations, create a new file with the name server.conf in $SPLUNK_HOME/etc/system/local/ 

• cxn_timeout: Timeout for establishing a TCP connection with the remote endpoint.
• rcv_timeout: Timeout for receiving a response after sending a request.
• send_timeout: Timeout for sending a request after establishing a connection.

Here's the updated configuration:

[clustering] 
cxn_timeout = 300 
rcv_timeout = 300 
send_timeout = 300

These changes provide Splunk with more time to complete network operations before they time out, which effectively resolved the issue of data buckets not being evicted properly.

Revision History

Revision	Publish Date	Comments
1.0	30-Sep-2026	Initial Release