fsck parallelism about greyhole HOT 1 CLOSED

Greyhole works on each file operation (executed on Samba) in sequence, using a queue system (operations get queued in /var/spool/greyhole first, then are moved into the tasks table in MySQL). So if you create fileA, then fileB, then rename fileA to fileB, it will work through those operations in the same order. It will never work on multiple file operations in parallel, because the order is very important.
fsck is different because it doesn't know about operations, it only knows about which files exist now. So if it finds a file that isn't where it should be, it will handle it as best as possible.

For fsck runs, the order in which folders & files are checked is undefined. I think it uses PHP's glob() function to walk through folders & files, which I think returns results sorted alphabetically.

For file copies specifically, there is a config named parallel_copying, which is true by default, which will use some cat | tee sorcery to create multiple files in parallel. This is used for normal processing by the daemon, and during fsck (as needed).
You can see parallel copying being used in the logs, which will appear as INFO write: Copying X.XXX KB file to: /mnt/hdd5/gh/ShareName/Folder/SomeFile, /mnt/hdd3/gh/ShareName/Folder/SomeFile, which lists all file copies being created simultaneously. (Of note: parallel copying logs the temporary filenames used to transfer; once the transfer completes, it will rename those temporary files using the real filename.)

from greyhole.