btrfs raid5 recovery with >1 half failed drive, or multiple drives kicked out at the same time.

btrfs raid5 recovery with >1 half failed drive, or multiple drives kicked out at the same time.

[Marc MERLIN]

I know the raid5 code is still new and being worked on, but I was
curious.

With md raid5, I can do this:
mdadm /dev/md7 --replace /dev/sde1

This is cool because it lets you replace a drive with bad sectors where
at least one other drive in the array has bad sectors, and the md layer
will read all drives for each stripe and write to a new drive.
The nice part is that it'll take the working parts of each drive, and as
long as no 2 drives have an unreadable sector for the same stripe, it
can recover.

I was curious, how does btrfs handle this situation, and more generally
drive failures, spurious multiple drive failures due to a bus blip where
you force the drives back online, and so forth?

Thanks,
Marc
-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/