The Effects of Filesystem Fragmentation

To measure the actual effects of the fragmentation level of a filesystem, we simulate heavy usage over a longer period of time on a constantly nearly full filesystem. We continuously create a number of fairly large but randomly sized files simultaneously while deleting other files to create storage space. We measure the fragmentation level of the filesystem and see how it evolves over time.

We compare various Linux filesystems by using Jens Axboe's blocktrace patch to monitor the activity at the level of the Linux kernel elevator (I/O scheduler) while running our simulated disk load. We have extended this patch to also gather the execution times of the actual requests at block I/O device level. With these measurements we calculate the data throughput, latency and power usage of the hard-disk drive.

Our simulate load is comparable to prolonged use of a Personal Video Recorders (PVR) application like MythTV. Such PVR devices will become commonplace in the near future, either running on a PC or as specialized Consumer Electronics (CE) devices. The number of broadcasted programs will also increase when Digital Video Broadcast (DVB) is being introduced on a large scale. A user will be able to program the PVR to record a large number of potentially interesting broadcasts, which automatically get deleted when storage is needed for newer recordings.