UFS2 metadata checksums
scott at bqinternet.com
Thu Apr 23 11:14:40 UTC 2009
I have spent some time writing a kernel module which calculates a
checksum of a UFS2 dinode structure and stores it in the reserved space
of the inode when writing it to disk. It is then verified when the
inode is read from disk. If the checksum verification fails, the read
returns an error (currently EIO).
I believe that protecting metadata integrity is important, especially as
storage capacity grows. Bitrot is a fact of life, and bad things can
happen if the kernel acts on a corrupted inode. Not only does this
module improve the stability of a server, but it also helps to prevent
additional damage to the filesystem that can be caused by metadata
I'm aware that data integrity issues are addressed with ZFS, but
unfortunately ZFS is still not yet suitable for many workloads. I'm
also aware that integrity checking can be done by using GELI between the
filesystem and the disk, but at a noticeable cost in performance and
space utilization. The method this module uses is fast and does not use
any additional space. Most importantly, it builds on mature code that
has worked well for decades.
Before I spend much more time on it, I have some questions:
1) Has anyone else done any work in this area?
2) Is there a demand for this in FreeBSD?
BQ Internet Corporation
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