mdstat - what is this?

[Michael Hipp]

What's the md255 stuff below? I didn't create any such device.

Thanks,
Michael

# cat /proc/mdstat
Personalities : [raid1]
md255 : active raid1 dm-4[1] dm-3[0]     <---
       136351616 blocks [2/2] [UU]        <---

md3 : active raid1 hdc2[1]
       18787904 blocks [2/1] [_U]

md2 : active raid1 hdc1[1]
       104320 blocks [2/1] [_U]

md1 : active raid1 hda4[0] hdc4[1]
       136351616 blocks [2/2] [UU]

md0 : active raid1 hda3[0] hdc3[1]
       1044160 blocks [2/2] [UU]