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ext4 and data lossext4 and data lossPosted Mar 12, 2009 11:03 UTC (Thu) by eru (subscriber, #2753)In reply to: ext4 and data loss by michaeljt Parent article: ext4 and data loss Why not just have a journal (metadata and data lumped together) with fixed blocks for data which does not yet have its own blocks? I believe this is more or less how a log-structured file system works: http://en.wikipedia.org/wiki/Log-structured_file_system. For some reason the idea is not in very common use.
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ext4 and data loss Posted Mar 12, 2009 11:11 UTC (Thu) by michaeljt (subscriber, #39183) [Link]
Indeed. Except of course that I was thinking more of a very short-lived log for data which would not otherwise be written back, rather than a full-blown log-structured file system.
ext4 and data loss Posted Mar 13, 2009 8:54 UTC (Fri) by michaeljt (subscriber, #39183) [Link]
In fact, one could sum up the idea as a mini-log filesystem on top of the normal filesystem, acting as a cache for things that can't immediately be written out to the real filesystem. Actually, I could imagine something like that existing outside of the actual filesystem code, but handled separately by the kernel, with the log either a pre-allocated file on the filesystem or a set of pre-allocated blocks on a swap device.
ext4 and data loss Posted Mar 13, 2009 0:23 UTC (Fri) by nix (subscriber, #2304) [Link]
Log-structured filesystems aren't in use for media on which seeks are
non-zero cost because they lead to fragmentation hell in short order. You don't always want to access your files in the same order in which you wrote them; they should be clustered differently. LFSes make that distinctly nontrivial to do.
ext4 and data loss Posted Mar 13, 2009 10:18 UTC (Fri) by job (guest, #670) [Link]
Perhaps LFSes will make a comeback with the SSDs, then?
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