Daniel Phillips <[email protected]> writes: > On Tuesday 16 December 2008 01:48, OGAWA Hirofumi wrote: >> > Clear the existent magic first, then overwrite: >> > >> > Yes, more sensible. Does MD really want us to clear 64 KB at the top >> > of the volume? That would seem rather sloppy of MD. Really, it >> > should rely on the just the final sector of a volume to know if it >> > is an MD volume. >> >> IIRC, MD RAID is using final 64kb. I think we should clear the top >> 1024bytes and final 64kb. (And with it, to make sure, we would check if >> volume size is bigger than 64kb, instead of clearing 64kb blindly.) > > Here is the full story about md superblock: > > http://lxr.linux.no/linux+v2.6.27/include/linux/raid/md_p.h#L19 > > As I read it, the MD superblock can be as much as 128K less a byte > below the top of the volume. It only actually uses 4K, and places that > 4K at a silly place for no apparent reason. This is really sloppy, > gross, disgusting, all that. But it is also existing practice. On the > other hand, if everybody has been thinking the md superblock is in the > top 64K and it actually isn't, do we do any harm by not attempting to > clear it? I think clearing out the space below our superblock (which > we have obligingly left free in case somebody needs to put a partition > block there) is a really good idea, but not so sure about the md stuff > at the top.
The end of volume has another reason, the block is also used by EFI partition. Well, we can ignore it though (instead, user have to delete it explicitly). -- OGAWA Hirofumi <[email protected]> _______________________________________________ Tux3 mailing list [email protected] http://mailman.tux3.org/cgi-bin/mailman/listinfo/tux3
