Comment 3 for bug 713267

Peter,

xtrabackup does close .ibd after copying them. So at any moment it only has up to 3 files open (with no --parallel): source, destination and the log file. It also doesn't use tablespace management functions from InnoDB (where innodb_open_files limit is checked), but instead opens and closes files using the lower-level file management functions.

So what I think actually happened is that the number of files open by the server + 3 (number of files open by xtrabackup) exceeded "ulimit -n" at some point. But that cannot be avoided by handling server/InnoDB file limits. Raising ulimit -n, however, should help, and it did.