On Mon, Sep 1, 2008 at 2:37 PM, Theodore Tso <tytso@xxxxxxx> wrote: > On Mon, Sep 01, 2008 at 01:18:31PM -0400, Mag Gam wrote: >> This maybe a newbie question but how come other file systems such as >> ReiserFS and Veritas' Vxfs dynamically allocate inodes and filesystems >> such as ext2/ext3 and JFS we need to allocate them when creating the >> filesystem? Is there a performance or maintenance gain when pre >> allocating? > > Having a static inode table is definitely much simpler than a dynamic > inode table, and that's why ext2 originally used a static inode > allocation system. Ext2 drew much of its initial design inspiration > from the BSD Fast Filesystem, and it (along with most traditional Unix > filesystems) used a static inode table. > > One of the advantages of having a static inode table is you can always > reliably find it. With a dynamic inode table, it can often be much > more difficult to find it in the face of filesystem corruption, caused > by either hardware or software failure. For example, with Reiserfs, > the inodes are stored in a B-Tree. If the root node, or a relatively > high-level node of the B-tree is lost, the only way to recover all of > the inodes is by looking at each block, and trying to determine if it > "looks" like part of the filesystem B-tree or not. This is what the > reiserfs's fsck program will do if the filesystem is sufficiently > damaged. Unfortuntaely, this means that if you store reiserfs > filesystem image (for example, for use by vmware, or qemu, or kvm, or > xen) in a reiserfs filesystem, and the filesystem gets damaged, the > recovery procedure will take every single block that looks like it > could have been part Reiserfs B-tree, and stich them together into a > new-btree. The result, if you have Reiserfs filesystem images is > those blocks will get treated as if they were part of the containing > filesystem, and the result is not pretty. > > These problems can be solved (although they were not for Reiserfs), > but it means a lot more complexity. > > - Ted > Ted, Thanks for the explanation and dumb-ing it down for me :-) So, if a reiserFs filesystem is damaged and it naturally do a fsck. The fsck basically recreated the b-tree by scanning from 1 to end of the filesystem? _______________________________________________ Ext3-users mailing list Ext3-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/ext3-users
