Re: RAID superblock....

[Neil Brown]

On Sunday March 10, [e-mail] wrote:
> 
> Hi,
> 
> The MD code I see doing: 
> 
> 
> 488         sb_offset = calc_dev_sboffset(rdev->dev, rdev->mddev, 1);
> 489         rdev->sb_offset = sb_offset;
> 490         fsync_dev(dev);
> 491         set_blocksize (dev, MD_SB_BYTES);
> 492         bh = bread (dev, sb_offset / MD_SB_BLOCKS, MD_SB_BYTES);
> 
> 
> where sb_offset is calculated as: 
> 
> 290         if (blk_size[MAJOR(dev)])
> 291                 size = blk_size[MAJOR(dev)][MINOR(dev)];

You missed:
	if (persistent)
		size = MD_NEW_SIZE_BLOCKS(size);

where MD_NEW_SIZE_BLOCKS is
#define MD_NEW_SIZE_BLOCKS(x)		((x & ~(MD_RESERVED_BLOCKS - 1)) - MD_RESERVED_BLOCKS)

and there you have your "-1".

> Anyway on the old machine, I still cannot find the raid superblock by
> hand, but the drives now mount, so the kernel must have been able to
> locate them somehow......

The superblock should be located between 64K and 128K from the end of
the device, on a 64K boundary.
> 

NeilBrown