very large data-offset?

[Duane <duane@xxxxxxxxxx>]

Why is the data offset set so big? I created a 3x4TB RAID5 array and the 
data offset was 128MB. Chunk size was the default 512kB.

I cannot see why such a large offset is used. I would think the data 
offset need only be at most the chunk size plus the space (1 sector) for 
the superblock and bitmap.

When reshaping the array, I am prompted to use an external file, so I 
don't see that mdadm ever uses the space.


I tried making some test arrays and got much smaller sizes. A 3x1GB 
RAID5 array with 64k chunks had a 1MB data offset.


If I make a 7x4TB RAID5 array with 64kB chunks, is there a problem with 
setting the data offset to around 2MB?


Thanks

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