On Wed, Mar 28, 2012 at 10:08:39AM -0600, Andreas Dilger wrote: > On 2012-03-27, at 8:47 AM, Yongqiang Yang wrote: > > Hi Ted, Andreas and List, > > > > As Andreas pointed out last year, if the last group is the 1st group > > in a meta bg, then its group desc has no backup. > > With meta_bg resizing inode is useless, I had a thought that we store > > a backup group descriptor of the last group in the resizing inode？ > > What's your opinions? It's an issue, however, when I originally thought about a number of years ago, it wasn't something I was terribly worried about, since by definition the percentage of the file system that we could lose is a small percentage overall. If we really were worried we could simply strongly bias the inode allocator against using the inods in that last block group. Alternatively, now that we have metadata checksums, it becomes even easier to find the inode table via a brute force search if we really needed to find it. > Actually, if the backup is always stored in the last block of the 0th > group (which is itself the last group in the filesystem), there isn't > even a need to store this location in the superblock. Something that might make sense is to put a backup of the block group descriptor at block #s_num_blocks (i.e., one block past the end of the file system as described in the superblock). E2fsck would just simply try to see if there's a valid block group descriptor block at one block past the end of the file system if the primary looks bad and there aren't any of the normal meta_bg backups --- and that way we wouldn't need to make any file system format changes. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
