Writing drives must be fed a constant stream of data during the writing process. If the writing drives does not constantly receive data at a rate suitable for the maximum write speed and buffer size, the writing process will fail and DiscJuggler will report errors such as a buffer under-run. While DiscJuggler can perform tests to minimize the number of such failures, there are common causes for these types of error. Your hard disk should have an access speed of under 15 milliseconds and be able to always transfer data faster than the maximum write speed (where 1x CD speed =~172 KB/sec, 1x DVD speed =~ 1.2 MB/sec). To be on the safe side, a hard disk's average transfer speed should provide a reasonable margin over the maximum write speed. The same speed requirements are applicable to any other source data device.

Heavy disk fragmentation can also slow the effective transmission rate of data to the writing drive, especially when writing from a disc image file. The regular use of a disk defragmentation software is highly recommended.