$ rm -f /tmp/a ; truncate -s 6366g /tmp/a ; mkfs.xfs -f /tmp/a -d agcount=3200 -l agnum=0 
meta-data=/tmp/a                 isize=512    agcount=3200, agsize=521503 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=1, sparse=1, rmapbt=0
         =                       reflink=1    bigtime=0 inobtcount=0
data     =                       bsize=4096   blocks=1668808704, imaxpct=5
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0, ftype=1
log      =internal log           bsize=4096   blocks=521492, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
mkfs.xfs: root inode created in AG 1, not AG 0