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Within OneFS, quota data is maintained in quota accounting blocks (QABs). Each QAB contains many quota accounting records, which need to be updated whenever a particular user adds or removes data from an area of the file system on which quotas are enabled (quota domain). If many clients are simultaneously accessing the quota domain, these blocks can become highly contended and a potential bottleneck. Similarly, if a single client (or small number of clients) consistently makes a large number of small writes to files within a single quota, write performance could again be impacted.
To address this issue, quota accounts have a mechanism to help avoid hot spots on the nodes storing QABs. Quota account constituents (QACs) help parallelize the quota accounting by including additional QAB mirrors distributed across other nodes in the cluster.
Configuration is managed through a sysctl, efs.quota.reorganize.qac_ratio, which increases the number of quota accounting constituents. This provides better scalability and reduces latencies on heavy create/delete activities when quotas are used.
Using this parameter, the internally calculated QAC count for each quota is multiplied by the specified value. If a workflow experiences write performance issues, and it has many writes to files or directories that are governed by a single quota, and then increasing the QAC ratio can significantly improve write performance.
The sysctl efs.quota.reorganize.qac_ratio can be reconfigured to its maximum value of 8 from its default value of 1 using the following CLI command:
# isi_sysctl_cluster efs.quota.reorganize.qac_ratio=8
To verify the persistent change, run:
# cat /etc/mcp/override/sysctl.conf | grep qac_ratio
efs.quota.reorganize.qac_ratio=8 #added by script
Although increasing the QAC count through this sysctl can improve performance on write-heavy quota domains, some amount of experimentation might be required until you find the ideal QAC ratio value. Adjusting the parameter can adversely affect write performance, if you apply a value that is too high or if you apply the parameter in an environment that does not have diminished write performance due to quota contention.
Also, OneFS provides a CLI command that can restripe the QABs to improve their performance:
# isi_restripe_qabs retune
This utility can be run either on demand or periodically to randomly redistribute QABs for all existing quotas. It does this by ignoring the default rebalance layout and running a retune layout strategy instead, thereby alleviating the performance impact from an imbalanced QAB layout.
For more information about OneFS commands and feature configuration, see the OneFS Administration Guide.