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Dear Lustre developers,</div>
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I am evaluating the use of `lfs migrate` to perform online OST data migration in a production environment where I/O activity must remain uninterrupted.</div>
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While reviewing the help output of the tool, I noticed the warning:</div>
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"(may be not safe with concurrent writes)"</div>
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After tracing the commit history, I found that this warning was introduced in the following patch:</div>
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https://review.whamcloud.com/c/fs/lustre-release/+/13754</div>
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Based on my reading of the implementation:</div>
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- When using the `--block` option, a group lock appears to be used to protect the migration operation.</div>
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- When using `--non-block`, a lease mechanism is in place, and migration is aborted if conflicting access is detected.</div>
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However, I would like to better understand the scenarios in which this operation may still be considered unsafe.</div>
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Could you kindly clarify the following:</div>
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1. Under what conditions does `lfs migrate` pose a risk when concurrent writes are happening?</div>
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2. Specifically, if client processes are appending to or modifying files during `--non-block` migration, what types of issues might arise (e.g., metadata corruption, partial migration, or data inconsistency)?</div>
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3. Is the `--block` option considered completely safe under concurrent write loads, or are there known edge cases where group locking may be insufficient?</div>
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Any technical explanation, known limitations, or recommended best practices would be greatly appreciated.</div>
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Thank you very much for your time and insights.</div>
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Best regards</div>
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