I am working on Ext3 and after looking at FS layout - ext3 reserves ~1024 blocks as Reserved Group Descriptor Table (reserved GDT blocks are between Group Descriptor blocks and Bitmap blocks).

These blocks are used once we do online resizing. I was wondering how these reserved blocks are used after online resizing is done? Are these free blocks used as data blocks or they can be used for other purposes as well?

Also, what is the impact (apart from the fact that online-resizing will not work) if we don't leave any room for reserved GDT?


The blocks are used for adding more group descriptors to the table, to describe the new groups added by the resize. Online resize is the only reason for the reserved space, and so the only thing you lose by not having it.

  • Thank you for clearing my doubt. Basically - if you use that space - you can grow less when you do online resizing. Suppose if you have 1024 blocks for GDT and each group descriptor is 32 bytes that means (4096/32 = 128 group descriptors per block) - so you can expand upto 128 * 1024 block groups. – yguw Jun 12 '15 at 23:14

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.