No space left on device, but the partition only half full and inodes are available

"No space left on device" can be a very missleading error. It can pop up on all sorts of write conditions other than having no disk space available.

Does that file already exist and is owned by someone else?

Do you have quotas enabled on this filesystem?

If you try to create another file in that filesystem manually (ie touch /src1/data/testfile) do you get the same error, or does it create the file?

Are you able to try creating a file as root?