OT - 2 of 4 drives in a Raid10 array failed - Any chance of recovery?

Sorry guys, I know this is very off-track for this list, but google hasn't
been of much help. This is my raid array on which my PG data resides.

I have a 4 disk Raid10 array running on linux MD raid.
Sda / sdb / sdc / sdd

One fine day, 2 of the drives just suddenly decide to die on me. (sda and
sdd)

I've tried multiple methods to try to determine if I can get them back
online.

1) replace sda w/ fresh drive and resync - Failed
2) replace sdd w/ fresh drive and resync - Failed
3) replace sda w/ fresh drive but keeping existing sdd and resync - Failed
4) replace sdd w/ fresh drive but keeping existing sda and resync - Failed

Raid10 is supposed to be able to withstand up to 2 drive failures if the
failures are from different sides of the mirror.

Right now, I'm not sure which drive belongs to which. How do I determine
that? Does it depend on the output of /prod/mdstat and in that order?

Thanks