Questions on RAID alignment

[Spelic]

Hello list
a few questions

1- Does XFS support alignment to concatenation RAIDs (e.g. linear over 
raid1) similarly to striped ones? I am guessing probably su and sw 
should not be specified and the agcount should be multiple of the number 
of the concatenated devices, is that correct?

2- Can mkfs parameters be altered after creation, e.g. after growing a 
RAID and then growing the XFS fs, can I also alter su, sw, agcount somehow?

3- I seem to remember there was an xattr that one could attach to /home 
(if /home was under XFS) so that every user (subdir of /home) would get 
a different AG in a different RAID device. I cannot find that 
information anymore on the internet; could you refresh my mind?

Thank you
Spelic