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I was reading Ext2 file system details, and I am not clear with the fact that the number of blocks in a block group is (b x 8) where b is the block size.

How have they arrived at this figure. What is the significance of 8.

RootPhoenix
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1 Answers1

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For each group in a filesystem ext2 there is a block bitmap, which keeps track of which blocks are used (bit equals 1) and which are still free (bit equals 0). This structure is designed to occupy exactly one block. Hence, the number of bits in the block bitmap is equal to b x 8, where b is the block size expressed in bytes.

Blocks in the group must not outnumber bits in the block bitmap - otherwise we would not be able to keep information on their availability. At the same time we want groups to manage maximal possible number of blocks in order to limit space occupied by metadata. Therefore, the number of blocks in the group equals the maximum: b x 8.

Polly Peachum
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