[Tux3] Review incoming changes

OGAWA Hirofumi hirofumi at mail.parknet.co.jp
Tue Dec 16 03:28:45 PST 2008

Daniel Phillips <phillips at phunq.net> 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 <hirofumi at mail.parknet.co.jp>

Tux3 mailing list
Tux3 at tux3.org

More information about the Tux3 mailing list