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On Tue, 24 Apr 2007, Nikita Danilov wrote: > Amit Gud writes: > > Hello, > > > > > This is an initial implementation of ChunkFS technique, briefly discussed > > at: http://lwn.net/Articles/190222 and > > http://cis.ksu.edu/~gud/docs/chunkfs-hotdep-val-arjan-gud-zach.pdf > > I have a couple of questions about chunkfs repair process. > > First, as I understand it, each continuation inode is a sparse file, > mapping some subset of logical file blocks into block numbers. Then it > seems, that during "final phase" fsck has to check that these partial > mappings are consistent, for example, that no two different continuation > inodes for a given file contain a block number for the same offset. This > check requires scan of all chunks (rather than of only "active during > crash"), which seems to return us back to the scalability problem > chunkfs tries to address. not quite. this checking is a O(n^2) or worse problem, and it can eat a lot of memory in the process. with chunkfs you divide the problem by a large constant (100 or more) for the checks of individual chunks. after those are done then the final pass checking the cross-chunk links doesn't have to keep track of everything, it only needs to check those links and what they point to any ability to mark a filesystem as 'clean' and then not have to check it on reboot is a bonus on top of this. David Lang > Second, it is not clear how, under assumption of bugs in the file system > code (which paper makes at the very beginning), fsck can limit itself > only to the chunks that were active at the moment of crash. > > [...] > > > > > Best, > > AG > > Nikita. > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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