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 point is, you _NEED_ to be sure that data written before the
superblock (or indeed anywhere further up the tree, you can make
changes in theory which don't require super-block updates) are written
firmly to the platters before any thing which refers to it is updated.
Alan was saying with IDE you cannot reliably do this, I assume you can
with SCSI was my point.
--cw
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