Many customers enquire about using EFS for Bitbucket Data Center. We should include a note in the FAQ describing why it's not suitable:

Clustering technical requirements

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Does Bitbucket Data Center clustering support EFS?

Not at this time. As noted in Amazon EFS Performance:

The distributed nature of Amazon EFS … results in a small latency overhead for each file operation. Due to this per-operation latency, overall throughput generally increases as the average I/O size increases, because the overhead is amortized over a larger amount of data.

Git typically involves many thousands of small file operations and the additional latency for each file operation means git is not suited to a distributed file system such as EFS.