Why does Synology DSM's "USB Copy" skip Umlaut-named files?

Question

Background

I have a large number of files from my mac that I first copied to a FAT32 hard drive and now migrated to a Synology NAS (DS216 with DSM 6 in my case, using ext4 internally) with rsync. I try to use Synology "USB Copy" to copy these files to another FAT32 USB volume. I would love to use this tool since it allows automatic triggering of copy jobs when a particular USB device gets connected.

Problem

USB Copy ends with a non-helpful error message

The USB Copy task My_Backup_Task on ds216 encountered unknown errors. The last error code is -10. Please try again or contact Synology Support for assistance.

When I compare the source and destination file trees, some files are missing especially with Umlauts (äöü) in them.

Any ideas of why this is and how to fix it?

Answer 1

This is a Bug in "USB Copy". OSX encodes Umlauts in a different way (NFD instead of NFC, see here and here). "USB Copy" is not able to deal with these names, it can only handle NFC encoded file names. Buried in the logs /var/log/usbcopyd.log.1.xz you can find something like

usb-copyd: [WARN] event-manager.cpp(192): EVENT is not NFC Form 'Event<EV_COPY> (WAITTING): [4] /path/filename_with_Umlaut_ä.JPG (file_op,file)', skipping...

... so they know they can't do this, but do not provide a helpful error message to the user :-(

A helpful workaround might be to use convmv to rename the files, according to this blog you might be successfull with

pkg install perl
wget http://www.j3e.de/linux/convmv/convmv-1.15.tar.gz
tar xzvf convmv-1.15.tar.gz
cd convmv-1.15/
sed -i -e 's/usr/opt/1p' convmv
/opt/bin/convmv/convmv -f iso-8859-1 -t utf8 --notest -r /volume1/yourpath

See also this SO question for more details.

According to this SF answer, you might also have avoided the problem when running rsync by using the --iconv option, e.g.

rsync -a --iconv=utf-8-mac,utf-8 localdir/ mynas:remotedir/

... but I am not sure if this is helpful when you have a mixed NFC / NFD directory tree.