Messages in this thread | | | From | "Albert D. Cahalan" <> | Subject | Re: [PATCH] 64 bit scsi read/write | Date | Sun, 15 Jul 2001 21:08:41 -0400 (EDT) |
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Daniel Phillips writes: > On Sunday 15 July 2001 05:36, Chris Wedgwood wrote: >> On Sat, Jul 14, 2001 at 10:11:30PM +0200, Daniel Phillips wrote:
>>> Atomic commit. The superblock, which references the updated >>> version of the filesystem, carries a sequence number and a >>> checksum. It is written to one of two alternating locations. On >>> restart, both locations are read and the highest numbered >>> superblock with a correct checksum is chosen as the new >>> filesystem root. >> >> Yes... and which ever part of the superblock contains the sequence >> number must be written atomically. > > The only requirement here is that the checksum be correct. And sure, > that's not a hard guarantee because, on average, you will get a good > checksum for bad data once every 4 billion power events that mess up > the final superblock transfer. Let me see, if that happens once a year,
In a tree-structured filesystem, checksums on everything would only cost you space similar to the number of pointers you have. Whenever a non-leaf node points to a child, it can hold a checksum for that child as well.
This gives a very reliable way to spot filesystem errors, including corrupt data blocks.
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