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?
These blocks are kept for future resizing, until the filesystem reaches 1024x the original formatted size, or the filesystem hits 16TB (at which point a different resizing method is used).
If you remove the
resize_inode feature, the blocks are freed, you could use them for data, and your filesystem can no longer be resized online at all, or "easily" offline (it will need to move any files using those blocks out of the way).
For the 4MB of space they consume, it is probably not worthwhile to remove this feature unless you know for a fact that you will never need to resize the filesystem.