Comment # 4 on bug 1230345 from Ruediger Oertel

broken case:
3460311 openat(AT_FDCWD, "/dev/zipl0000", O_RDWR) = 4
3460311 ioctl(4, BLKFLSBUF)             = 0
3460311 lseek(4, 0, SEEK_SET)           = 0
3460311 read(4,
"zIPL\0\0\0\1\0\0\0\0\0\0\0\0\0\0\0\0\0\0\200\10\2\0\0\0\0\0\0\0"..., 512) =
512

working case:
3467985 openat(AT_FDCWD, "/dev/zipl0000", O_RDWR) = 4
3467985 ioctl(4, BLKFLSBUF)             = 0
3467985 lseek(4, 0, SEEK_SET)           = 0
3467985 read(4,
"zIPL\0\0\0\1\0\0\0\0\0\0\0\0\0\0\0\0\0x`\2\2\0\0\0\0\0\0\0"..., 512) = 512

checking /dev/sdb vs /dev/mapper/3600507630bffd2160000000000002000 

in both cases same output:
s390zl21:~ # dd if=/dev/sda of=test1 bs=256 count=1
1+0 records in
1+0 records out
256 bytes copied, 5.3152e-05 s, 4.8 MB/s

s390zl21:~ # xxd test1
00000000: 7a49 504c 0000 0001 0000 0000 0000 0000  zIPL............
00000010: 0000 0000 0078 4062 0200 0000 0000 0000  .....x@b........
00000020: 0000 0000 0000 0000 0000 0000 0000 0000  ................