Bug 1396253

There are two ways to create a "raid1" LV:
1) use the lvcreate command to create the whole thing at once
2) use the lvconvert command to "upconvert" from a linear LV

The way that initialization happens in RAID can be problematic for #2 if there is a primary device failure during the process.  After encountering a failure (read, write, or entire device) in the primary device, the sync process simply continues on using an alternate device to complete the sync.  This is odd but not an issue with #1; however, in the case of #2 it can lead to data loss - even if the primary device is not replace and later revived.

Imagine three devices.  The first device is filled with 'A's, the second with 'B's and the third with 'C's.  Before the sync begins, the three disks would look like:
 A B C <- 2nd half of the disks
 A B C <- 1st half of the disks
Let's say the first device dies at the moment the first half of the addressable space is sync'ed.  We would then have the following (where [] signifies the dead device):
 [A] B C
 [A] A A
The sync process will simply continue, using the next available device after marking the first device as 'failed'.  The final result will be:
 [A] B B
 [A] A A
If the primary device can be revived at this point, it is synchronized according to the rest of the copies, leaving:
 B B B
 A A A
Again, this is fine for a "raid1" that was created from scratch - the contents are perfectly in-sync.  However, if the array was being upconverted from a linear LV, the last half of the original contents is destroyed by the process of recovery when the device is revived.  In the case of #2, we would much rather have the recovery process stop when the primary fails - giving the user a chance to revive it (remember, it could have happened due to something as simple as a single read/write error).  Once revived, the desire would be to continue syncing from the original LV.