Re: data corruption using raid0+lvm2+jfs with 2.6.0-test3

[Mike Fedyk]

On Sun, Aug 17, 2003 at 10:12:27AM +1000, Neil Brown wrote:
> On Saturday August 16, mfedyk@xxxxxxxxxxxxx wrote:
> > I have a raid5 with "4" 18gb drives, and one of the "drives" is two 9gb
> > drives in a linear md "array".
> > 
> > I'm guessing this will hit this bug too?
> 
> This should be safe.  raid5 only ever submits 1-page (4K) requests
> that are page aligned, and linear arrays will have the boundary
> between drives 4k aligned (actually "chunksize" aligned, and chunksize
> is atleast 4k). 
> 

So why is this hitting with raid0?  Is lvm2 on top of md the problem and md
on lvm2 is ok?

> So raid5 should be safe over everything (unless dm allows striping
> with a chunk size less than pagesize).
> 
> Thinks: as an interim solution of other raid levels - if the
> underlying device has a merge_bvec_function which is being ignored, we
> could set max_sectors to PAGE_SIZE/512.  This should be safe, though
> possibly not optimal (but "safe" is trumps "optimal" any day).

Assuming that sectors are always 512 bytes (true for any hard drive I've
seen) that will be 512 * 8 = one 4k page.

Any chance sector != 512?
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