MP All Models Is it damaging to turn off a hard drive that's mounted without ejecting it first?

[machenryr]

I don't guess this is a Mac Pro question in particular, but it's a question I've had for a while. Is it really damaging to turn off an external drive or pull out a memory card without ejecting it first? It's just a lazy question really.

 

[jbarley]

There is always the possibility of data loss.
Ejecting the the drive completes any and all disk activity, then closes any open files, making it safe to power down and remove the drive.

 

[machenryr]

There is always the possibility of data loss.
Ejecting the the drive completes any and all disk activity, then closes any open files, making it safe to power down and remove the drive.

Thank you. But is it just disk activity? If I know for a fact that all disck activity is done is it still harmful potentially?

 

[MarkC426]

I think it is just safer to eject first.
Anything to avoid corruption.
Even though you may have closed any files, Mac OS may still be doing something in the background.

 

[ondioline]

Thank you. But is it just disk activity? If I know for a fact that all disck activity is done is it still harmful potentially?

It really depends on the filesystem. Unmounting (ejecting) a disk basically blocks any further operations and calls a final sync. That means it will flush out any buffers to the disk. Some old filesystems postpone journal writes until certain triggers are met, so if you shut down before that happened you'd lose everything that hadn't been synced.

You probably don't need to worry about APFS though, it's a copy on write filesystem. It's mostly a concern for journal-less and older filesystems like fat