Why is sb->size set to 0 with raid0?

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Hello,

while examining a raid0 v1.2 superblock I found "Used Dev Size" seems
not to be set there, mdadm -E on a component device shows:
	          Magic : a92b4efc
	        Version : 1.2
	    Feature Map : 0x0
	...
	 Avail Dev Size : 2930274824 (1397.26 GiB 1500.30 GB)
	  Used Dev Size : 0
	    Data Offset : 16 sectors
	   Super Offset : 8 sectors
	          State : clean

Is this intentional?
This is just to let you know and for my curiosity. I don't know whether
this has negative side-effects or not. I found none until now.

Don't get me wrong, I like the (IMHO positive) side-effect of this: it
makes totally sense to me, not to reserve bitmap-space for raid0 - I
even downgraded to mdadm 3.1.1 for raid creation to get rid of the 1M
alignment, and I was short thinking about patching super1.c for this
array to get rid of the bitmap-space reservation as well.
Thus, I was just positively surprised to see that in fact there *is* no
bitmap-space reserved for raid0, wondered how and where this was
managed, and tracked it down to sb->size being set to 0.


regards
   Mario
-- 
You know, people think mathematics is complicated. Mathematics is the simple
bit. Its the stuff we can understand. Its cats that are complicated. I mean,
what is it in those little molecules and stuff that make one cat behave
differently than another, or that make a cat? And how do you define a cat?
I have no idea.                                 -- John Conway

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