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Within OneFS, quota data is maintained in Quota Accounting Blocks (QABs). Each QAB contains a large number of Quota Accounting records, which need to be updated whenever a particular user adds or removes data from a file system on which quotas are enabled. If a large number of clients are accessing the file system simultaneously, these blocks can become highly contended and a potential bottleneck.
To address this issue, quota accounts have a mechanism to avoid hot spots on the nodes storing QABs. Quota account Constituents (QACs) help parallelize the quota accounting by including additional QAB mirrors on other nodes.
By default, QAC ratio is set to 1.
The following sysctl increases the number of quota accounting constituents, which allows for better scalability and reduces latencies on create/delete flurries when quotas are used.
Using this parameter, the internally calculated QAC count for each quota is multiplied by the specified value. If workflow experiences write performance issues, and it has many writes to files or directories governed by a single quota, increasing the QAC ratio (efs.quota.reorganize.qac_ratio) might improve write performance.
The QAC ration can be changed to value 8 from the default value of 1 by running the following OneFS CLI command:
isi_sysctl_cluster efs.quota.reorganize.qac_ratio=8
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.