Zbr's days.

About :: TODO :: Blog :: RSS :: Old blog :: Projects :: GIT :: Gallery :: Notes

Tue, 27 Feb 2007

Ext4 extents will (probably) support block checksumming. [ND]

Andreas Dilger wrote:

In the ext4 extents format there is the ability (not implemented yet) to add some extra information into the extent index blocks (previously referred to as the ext3_extent_tail). This is planned to be a checksum of the index block, and a back-pointer to the inode which is using this extent block.

This allows online detection of corrupt index blocks, and also detection of an index block that is written to the wrong location. There is as yet no plan that I'm aware of to have in-filesystem checksums of the extent data.
I plan to have such a block in each inode/data block not only extents, unfortunately it is impossible to implement for existing systems without on-disk format changes, so only extents will be protected by checksums in ext4.

Interesting note later presented by Oracle engneer Martin Petersen about how data integrity is managed in modern hardware, but filesystem checksums are not about corrupted disks, but about corrupted files on perfectly correct hardware.

/devel/fs :: Link / Comments ()