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An example of the error: The application does a buffered write and receives success. (This means data can be stored in file system cache, non-stable media.) An fsync/fdatasync is used to make sure the data is stored in stable media. The stable media write(s) occurs during the sync operation and can fail for any number of reasons (out of disk space, lost connectivity to SAN, etc.) reporting an EIO error.
The issue, as described in the link, is that