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I am moving my Ubuntu install to lvm over raid 1. I created the arrays with only 1 disk initially, planning to add the second disk later. I got the files moved and the system booted up succesfully on the new disk, but the arrays and paritions seemed to have changed names. Initially I partitioned the disk as follows:

Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          20      153600   fd  Linux raid autodetect
/dev/sda2              20      243202  1953359960   fd  Linux raid autodetect

I then created 2 degraded raid arrays, corresponding to these partitions, md0 for /boot and md1 for lvm with everything else on it. After installing grub and booting from the new disk, everything seems to work except that weird things are afoot. /dev/md1 has partions on it even though I all I did was pvcreate /dev/md1:

Device Boot      Start         End      Blocks   Id  System
/dev/md1p1   *         257       38656      153600   fd  Linux raid autodetect
/dev/md1p2           38657   488378646  1953359960   fd  Linux raid autodetect

Additionally, /proc/mdstat shows (I have already added the second disk):

md0 : active raid1 sdc1[1] md1p1[0]
      153536 blocks [2/2] [UU]

md1 : active raid1 sdc2[2] sda[0]
      1953359872 blocks [2/1] [U_]

Where did md1p1 come from, and why doesn't /proc/mdstat show sda1 and sdc1, and sda2 and sdc2?

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A late reply, but hey:

Unfortunately you didn't show the relevant parts, for example, which units your fdisk output shows (sectors? cylinders?)

Nonetheless it looks like you got bitten by the bug of the 0.90 meta data block:

0, 0.90 

Use the original 0.90 format superblock. This format limits arrays to 28 component devices and limits component devices of levels 1 and greater to 2 terabytes. It is also possible for there to be confusion about whether the superblock applies to a whole device or just the last partition, if that partition starts on a 64K boundary.

That means if you have a 0.90 meta data block on the last partition, and it starts on a 64k boundary, mdadm will assume the whole disk belongs to the raid. What you're seeing is the partition table of /dev/sda within the RAID. Of course this will give you massive corruption if you try to access anything within that RAID.

Upgrade ASAP (I can speak out of experience).

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