I've formatted a new filesystem with and without extents feature just to understand how this feature works. However, when I look at the inode field i_flags I see that this field always has zero value (for "used" inodes 2, 7 and 11).
Documentation (from Kernel.org) about extents says, that this flag should have 0x80000 bit set for inodes which use extents – but it looks like it's not accurate.
Can I have inodes with and without extents in the same filesystem? Should I rely on the i_flags to determine the way, how the i_block field is used? Or it is just one filesystem-wide flag in the superblock which dictates extents usage for all inodes?
Best Answer
The
extentsflag is stored for each inode, so it is possible to upgrade an ext3 filesystem without extents to ext4, and then enable theextentsfeature in the superblock and new inodes would be created withextentsenabled. You should definitely check the per-inode flag to decide howi_blocksis being used for each file.