RE: LVM on md0: raid0_make_request bug: can't convert block acros s chunks or bigger than 64k

RE: LVM on md0: raid0_make_request bug: can't convert block acros s chunks or bigger than 64k

[Karl Vogel]

> > Somebody else referred to this posting:
> >   http://marc.theaimsgroup.com/?l=linux-kernel&m=103369952814053&w=2
> > 
> > but that patch doesn't apply cleanly anymore and I'm not 
> familiar with
> > the code to be confident to fix it up myself. (that post 
> was from almost
> > exactly 1 year ago, so alot changed probably :)
> 
> That patch is already included.
> 
> The problem is that dm is not honouring the merge_bvec_fn that
> raid0 has set.
> 
> This patch might fix it, but I'm not very familiar with the dm code,
> so I make no promises.

I will give it a shot when I get home.

> (I wonder why you are running LVM on top of raid0 given that lvm
> contains raid0 functionality).
> 
> NeilBrown

Historical reasons.. but since it worked, I never changed it.. and now it
makes for a good test case :)

Thx,
Karl

Re: LVM on md0: raid0_make_request bug: can't convert block acros s chunks or bigger than 64k

[Neil Brown]

On Saturday October 25, karl.vogel@seagha.com wrote:
> 
> 
> I noticed in the 2.6.0-test9 notes the following:
> 
> ---
> Neil Brown:
>   o md -  Use sector rather than block numbers when splitting raid0
>     requests
> ---
> 
> I'm not sure if this is related to the problem I was experiencing?!
> Anyway this doesn't fix the problem I was having. I still get the errors
> with -test9. Above patch to dm-table.c works for me.
> 
> Just thought I'd mention this..
> 
This addresses a different problem: raid0 would not correctly handle
some requests that are not 1K aligned.  XFS does some non-1K-aligned
requests where reading it's journal and caught this bug.
It has nothing to do with LVM or your problem.

NeilBrown

Re: LVM on md0: raid0_make_request bug: can't convert block acros s chunks or bigger than 64k

[Karl Vogel]

On Tue, 2003-10-21 at 02:09, Neil Brown wrote:

> The problem is that dm is not honouring the merge_bvec_fn that
> raid0 has set.
> 
> This patch might fix it, but I'm not very familiar with the dm code,
> so I make no promises.
> 
> (I wonder why you are running LVM on top of raid0 given that lvm
> contains raid0 functionality).
> 
> NeilBrown
> 
> 
> 
>  ----------- Diffstat output ------------
>  ./drivers/md/dm-table.c |    5 +++++
>  1 files changed, 5 insertions(+)
> 
> diff ./drivers/md/dm-table.c~current~ ./drivers/md/dm-table.c
> --- ./drivers/md/dm-table.c~current~	2003-10-21 10:05:29.000000000
> +1000
> +++ ./drivers/md/dm-table.c	2003-10-21 10:06:27.000000000 +1000
> @@ -489,6 +489,11 @@ int dm_get_device(struct dm_target *ti, 
>  		rs->max_sectors =
>  			min_not_zero(rs->max_sectors, q->max_sectors);
>  
> +		if (q->merge_bvec_fn)
> +			rs->max_sectors =
> +				min_not_zero(rs->max_sectors,
> PAGE_SIZE>>9);
> +			
> +
>  		rs->max_phys_segments =
>  			min_not_zero(rs->max_phys_segments,
>  				     q->max_phys_segments);


I noticed in the 2.6.0-test9 notes the following:

---
Neil Brown:
  o md -  Use sector rather than block numbers when splitting raid0
    requests
---

I'm not sure if this is related to the problem I was experiencing?!
Anyway this doesn't fix the problem I was having. I still get the errors
with -test9. Above patch to dm-table.c works for me.

Just thought I'd mention this..