Quoting Adam Borowski (kilob...@angband.pl): [enabling metadata checksums on relatively old ext4 filesystems:]
> Thus, if you created your filesystem with mkfs.ext4 older than > stretch/ascii, it's vital that you do the following, on an unmounted > filesystem (ie, need to boot from alternate media if it's /): > > resize2fs -b $DEV > tune2fs -O metadata_csum $DEV > fsck.ext4 -D $DEV First, thank you. We're all richer for this sharing of knowledge. https://ext4.wiki.kernel.org/index.php/Ext4_Disk_Layout clarifies what this specific command sequence is about: the '64bit' feature and its connection to block size and to the metadata checksum option: By default a filesystem can contain 2^32 blocks; if the '64bit' feature is enabled, then a filesystem can have 2^64 blocks. [...] Some [hisorical ext4] data structures did not have space to fit a full 32-bit checksum, so only the lower 16 bits are stored. Enabling the 64bit feature increases the data structure size so that full 32-bit checksums can be stored for many data structures. However, existing 32-bit filesystems cannot be extended to enable 64bit mode, at least not without the experimental resize2fs patches to do so. One gathers that the 'experimental resize2fs patches' have been merged since the above was written. Existing filesystems can have checksumming added by running tune2fs -O metadata_csum against the underlying device. [...] So, 'resize2fs -b [devicename]' turns on the filesystem's 64bit feature, rewriting ext4 metadata in a way that makes adequate room for storing full 32-bit checksums on all file metadata structures instead of just the lower 16 bits -- with the minor drawback of making the ext4 filsystem unmountable by systems with pre-3.6 kernels. Having done this house-cleaning, now you can do the second command that toggles on the metadata checksum option. Last, 'fsck.ext4 -D [devicename' 'optimises' (reindexes, or sorts and compresses) all directories. -- Cheers, "Like running into a burning building and trying to put the Rick Moen fire out by means of interpretive dance." -- Iain M. Banks r...@linuxmafia.com on alternative cancer treatments, after his own diagnosis McQ! (4x80) www.theguardian.com/books/2013/jun/15/iain-banks-the-final-interview _______________________________________________ Dng mailing list Dng@lists.dyne.org https://mailinglists.dyne.org/cgi-bin/mailman/listinfo/dng
