How to format RAID1 correctly

[Helmut Tessarek <tessarek@evermeet.cx>]

The information provided in the FAQ and on several web sites is not really
useful regarding RAID1.

According to the FAQ (entry 35):
The correct options to format a RAID1 (2 disks) with 64k chunk size is:
mkfs.xfs -d su=64k -d sw=1 /dev/mapper/data
But it also states that it would be automatically detected and used correctly,
yet
mkfs.xfs /dev/mapper/data
yields a different result:

[root@atvie01s ~]# mkfs.xfs -f /dev/mapper/data

meta-data=/dev/mapper/data       isize=256    agcount=4,
agsize=244173876 blks
         =                       sectsz=4096  attr=2, projid32bit=1
         =                       crc=0        finobt=0
data     =                       bsize=4096   blocks=976695504, imaxpct=5
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=0
log      =internal log           bsize=4096   blocks=476902, version=2
         =                       sectsz=4096  sunit=1 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0

Formel 1:

[root@atvie01s ~]# mkfs.xfs -f -d su=64k -d sw=1 /dev/mapper/data

meta-data=/dev/mapper/data       isize=256    agcount=32,
agsize=30521728 blks
         =                       sectsz=4096  attr=2, projid32bit=1
         =                       crc=0        finobt=0
data     =                       bsize=4096   blocks=976695296, imaxpct=5
         =                       sunit=16     swidth=16 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=0
log      =internal log           bsize=4096   blocks=476902, version=2
         =                       sectsz=4096  sunit=1 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0


Another inconsistency is that RAID1 doesn't use striping, so the chunk size
should be irrelevant in the first place.

So what is ultimately the correct way to format a RAID1?

Cheers,
  K. C.

-- 
regards Helmut K. C. Tessarek
lookup http://sks.pkqs.net for KeyID 0xC11F128D

/*
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