linux raid0建立问题-----------为什么 No such file or directory?

[cainiao000]

Disk /dev/sdb: 32.2 GB, 32212254720 bytes
255 heads, 63 sectors/track, 3916 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xdf0af0f9

Device Boot Start End Blocks Id System
/dev/sdb1 1 262 2104483+ fd Linux raid autodetect
/dev/sdb2 263 524 2104515 fd Linux raid autodetect
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[root@localhost wxb]# mdadm -C /dev/md0 -a yes -l 0 -n 2 /dev/sdb{1,2}
mdadm: cannot open /dev/sdb1: No such file or directory
[root@localhost wxb]# mdadm -C /dev/md0 --level=0 --raid-devices=2 /dev/sdb1 /dev/sdb2
mdadm: cannot open /dev/sdb1: No such file or directory
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为什么建立不成功？哪里出错了？