On Monday June 19, liudows2@xxxxxxxxx wrote:
> We can imagine that there is a raid0 array whose layerout is drawn in the
> attachment.
> Take this for example.
> There are 3 zones totally, and their zone->nb_dev is 5,4,3 respectively.
> In the raid0_make_request function, the var block is the offset of bio in
> kilobytes.
>
>
> x = block >> chunksize_bits;
> tmp_dev = zone->dev[sector_div(x, zone->nb_dev)];
>
> If block is in the chunk 5, then x = block >> chunksize_bits = 5.And the
> nb_dev of zone2 is 4.
> So tmp_dev = zone->dev[sector_div(5,4)] = zone->dev[1].
> But we can see that the right result should be zone->dev[0].
> Then how does the 'bug' get the right underlying device?
When you say 'right' result, you really mean 'expected' result.
You expect the layout to be
0 1 2 3 4
5 6 7 8
9 10 11
The actual layout for Linux-md-raid0 is
0 1 2 3 4
8 5 6 7
9 10 11
Not what you would expect, but still a valid layout.
NeilBrown
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