nixCraft

Hi,
I have a doubt as how many redundant backups of superblock are created in the file system ? Is it made on every block group or only on initial few block groups ?
In the filesystem that I created of size 128 MB with 16 block groups, when I run the dumpe2fs command on it, it gives the info on superblocks (These are not the exact wordings of the output ) :
primary superblock is present on block group 0,
back up superblock is present on block group 1, 3, 5, 7, 9.
Similarly for a file system with 256 MB size and 31 block groups, primary superblock is present on block group 0 and backups are present on block groups 1,3,5,7, and 9.
So my doubt is how does the file system decide how many backups of the superblock to be created ?
And the same doubt for block group descriptors as well. Block group descriptors are not present in each block group but only in the block groups where superblock is present.
Hoping for an earliest response.

Thanks,
Swapnil

mke2fs block-size is heuristically determined by the file system size and the expected usage of the filesystem. So you don't have to worry about it. It is calculated by mke2fs command. You can pass -n option to see exact location. Some old UNIX version has option to specify super block size.

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