Re: [dm-devel] [ANNOUNCE] multipath-tools-0.1.6

[Mike Tran <mhtran@us.ibm.com>]

On Tue, 2004-04-27 at 05:09, thornber@redhat.com wrote:
> On Tue, Apr 27, 2004 at 11:57:58AM +0200, christophe.varoqui@free.fr wrote:
> > Selon thornber@redhat.com:
> > 
> > > On Sun, Apr 25, 2004 at 11:54:59PM +0200, christophe varoqui wrote:
> > > > * add the dmadm WIP tool (read MD superblocks and create
> > > >   corresponding devmaps when possible)
> > > 
> > > :)
> > > 
> > Any insight on where to put the log of the mirror target when mapping over a
> > MD-created raid1 ?
> 
> MD effectively uses a log with a single region in it.  So we only need
> 3 sectors (2 for the header 1 for the bitset) for the log, is there
> any space in the MD metadata where this could be placed ?
> 
> - Joe

The MD device size is 64K aligned and MD superblock size is 4K.  In term
of sectors, the calculation is as follows:

MD_SB_BYTES 4096
MD_SB_SECTORS (MD_SB_BYTES / 512)

// x is the child device size in sectors.

#define MD_RESERVED_BYTES (64 * 1024)
#define MD_RESERVED_SECTORS (MD_RESERVED_BYTES / 512)
#define MD_NEW_SIZE_SECTORS(x) (((x) & ~(MD_RESERVED_SECTORS -1)) - MD_RESERVED_SECTORS)

It's safe to write the log after the MD superblock.

Regards,
Mike T.