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Re: UFS2 metadata checksums



On Thu, 23 Apr 2009 06:54:51 -0400
Scott Burns <scott_(_at_)_bqinternet_(_dot_)_com> wrote:

> Hi guys,
> 
> 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 corruption.
> 
> 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?
> 

This is actually something I would love to have in the base system,
but inodes are not the only structures that need the integrity
protection. Pretty much every other metadata block, from cylinder group
blocks to indirect blocks for files need similar protection for
this to be of real use.

--
Alexander Kabaev

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