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

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

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Microsoft is to operating systems ....
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