Re: [RFC] TileFS - a proposal for scalable integrity checking

["Jörn Engel" <joern@lazybastard.org>]

On Sun, 29 April 2007 20:40:42 -0500, Matt Mackall wrote:
> 
> So we should have no trouble checking an exabyte-sized filesystem on a
> 4MB box. Even if it has one exabyte-sized file! We check the first
> tile, see that it points to our file, then iterate through that file,
> checking that the forward and reverse pointers for each block match
> and all CRCs match, etc. We cache the file's inode as clean, finish
> checking anything else in the first tile, then mark it clean. When we get
> to the next tile (and the next billion after that!), we notice that
> each block points back to our cached inode and skip rechecking it.

How would you catch the case where some block in tile 2 claims to belong
to your just-checked inode but the inode has no reference to it?

How would you catch the inode referencing the same block twice with just
4MB of memory?

I believe you need the fpos field in your rmap for both problems.

Jörn

-- 
Anything that can go wrong, will.
-- Finagle's Law
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