Q&A: NASty errors

Q We use a mirrored external NAS to back up, then periodically write completed projects to DVD. When I try to trash the files after transferring them to DVD, level 3 folders and files cannot be trashed, the Finder reporting that they are still in use. I then have to erase their contents individually. Why is this?

A This is probably a problem in the Network-Attached Storage (NAS) system.

When files are written to, or still being read, the file system marks them as being in use. Each drive in your NAS has a data buffer, which must be flushed to disk to complete write operations. That flushing may not be occurring for some time afterwards.

Furthermore, within a mirrored RAID setup, both parts of the mirror must complete file operations and synchronise before you can remove those files. As your NAS does not use the Mac Extended (HFS+) file system natively, but its driver provides an emulation, that driver could be at fault – and that should be your first suspect. Report this to its support line and see what they have to say about it. You may find that a firmware or software update is already available to fix it.

Updated from the original, which was first published in MacUser volume 29 issue 3, 2013.