Specifications

Figure 2: MCS-DR PC System Software Overview
Initial tests with the ext2 file system yielded inconsistent results. Consequently, we implemented
a custom file system based on raw access to the drive array. The file system used by the software
is a flat file system with a simple bitmap structure written to the beginning of the drive, and the
remaining space available for file storage. The current (validated) file system supports as many as
1023 recordings, all of which combined may be up to 4.9 TiB in size. The file system can be easily
modified to support an arbitrarily large number of files.
The benefits of using a raw file system are two-fold. Bypassing the ext2 file system allows
writing contiguously without having to periodically update inodes and inode tables. Also, it allows
rapid file deletion, and formatting – operations that could take hours with ext2. Because speed is
critical, kernel caching is disabled for file reads and writes. The Linux kernel’s caching algorithms
are optimized for random access, but data streams are recorded sequentially. Tests with caching
enabled were unable to meet the rate requirement. Tests with caching disabled, however, were able
to meet and exceed the requirements.
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