For discussion on the Linux kernel developer mailing list Patches have been published with the implementation of the BeamFS file system using encoding Rida – Solomonto identify and recover damaged data in-place in single-drive configurations. The main applications of BeamFS are on-board computers of satellites, equipment in radiation therapy rooms and other systems operating in high radiation conditions, for which the return of corrupted data is more critical than the inability to read the information.
By default, BeamFS can recover up to 8 lost bytes in each 255-byte block with an overhead of 7% (288 bytes of recovery codes for every 4096 bytes stored data). Error correction codes are used not only for data, but also for service information in the superblock, inode, directory indices and bitmaps. Integrity checks and attempts to recover missing data are carried out with each read operation. If the correctness of the information cannot be guaranteed, the operation ends with the error “-EIO”, which excludes the hidden return of damaged data.
Experiments showed that when the i.MX 8M Plus board with Linux and ext4 file system was irradiated with protons with energies from 20 to 58 meV, 90% of all failures occurred at the level of the file system and storage device drivers. We also simulated single bit distortions when reading from the media, BeamFS and Btrfs successfully recognized data corruption and always returned an error, while ext4 and ext3 silently returned the corrupted data.
BeamFS ensures integrity and recovery only at the stage from reading from the physical media to transferring it to the page cache in RAM. Storage integrity in RAM must be ensured by the use of error-correcting memory chips.
Among the limitations of BeamFS, there is a lack of support for journaling and Copy-on-Write (CoW) mode – metadata is written to the drive out of order, so in case of incorrect shutdown, a full check using fsck is required.
In addition to BeamFS, two more file systems were recently proposed for the Linux kernel: