hardware raid and xfs

[Alexander Mestiashvili <mailatgoogl@gmail.com>]

Hi Debian folks,

Could anyone please explain me why does this warning appear?

mkfs.xfs: Specified data stripe width 640 is not the same as the volume
stripe width 2048

How does xfs know about volume stripe size width ?

here is the command:
mkfs.xfs -fb size=4k -d su=64k,sw=5 /dev/mapper/mpath2
mkfs.xfs: Specified data stripe width 640 is not the same as the volume
stripe width 2048
meta-data=/dev/mapper/mpath2     isize=256    agcount=32,
agsize=12702944 blks
         =                       sectsz=512   attr=2, projid32bit=0
data     =                       bsize=4096   blocks=406494128, imaxpct=5
         =                       sunit=16     swidth=80 blks
naming   =version 2              bsize=4096   ascii-ci=0
log      =internal log           bsize=4096   blocks=198496, version=2
         =                       sectsz=512   sunit=16 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0


storage is hardware raid (hp msa g3)
The LUN allocated to the server is combined from 7 disks in raid6 (I
know it is not optimal for r6, 6+2 would be better),
chunk size is 64k
device is visible as /dev/mapper/mpath2 because of device mapper and
multipathing.

so the formula for mkfs.xfs seem to be correct: su=chunk size(64k),
sw=number of data disks (7-2)

Am I missing something ?

Thank you in advance,
Alex