On Monday 25 June 2001 00:54, Albert D. Cahalan wrote:
> By dumb luck (?), FAT32 is compatible with the phase-tree algorithm
> as seen in Tux2. This means it offers full data integrity.
> Yep, it whips your typical journalling filesystem. Look at what
> we have in the superblock (boot sector):
>
> __u32 fat32_length; /* sectors/FAT */
> __u16 flags; /* bit 8: fat mirroring, low 4: active fat */
> __u8 version[2]; /* major, minor filesystem version */
> __u32 root_cluster; /* first cluster in root directory */
> __u16 info_sector; /* filesystem info sector */
>
> All in one atomic write, one can...
>
> 1. change the active FAT
> 2. change the root directory
> 3. change the free space count
>
> That's enough to atomically move from one phase to the next.
> You create new directories in the free space, and make FAT
> changes to an inactive FAT copy. Then you write the superblock
> to atomically transition to the next phase.
Yes, FAT is what inspired me to go develop the algorithm. However, two
words: 'lost clusters'. Now that may just be an implemenation detail ;-)
--
Daniel
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