Re: How does btrfs handle bad blocks in raid1?

[Austin S Hemmelgarn <ahferroin7@gmail.com>]

On 2014-01-09 13:08, Chris Murphy wrote:
> 
> On Jan 9, 2014, at 5:41 AM, Duncan <1i5t5.duncan@cox.net> wrote:
>> Having checksumming is good, and a second 
>> copy in case one fails the checksum is nice, but what if they BOTH do?
>> I'd love to have the choice of (at least) three-way-mirroring, as for me 
>> that seems the best practical hassle/cost vs. risk balance I could get, 
>> but it's not yet possible. =:^(
> 
> I'm on the fence on n-way. 
> 
> HDDs get bigger at a faster rate than their performance improves, so rebuild times keep getting higher. For cases where the data is really important, backup-restore doesn't provide the necessary uptime, and minimum single drive performance is needed, it can make sense to want three copies.
> 
> But what's the probability of both drives in a mirrored raid set dying, compared to something else in the storage stack dying? I think at 3 copies, you've got other risks that the 3rd copy doesn't manage, like a power supply, controller card, or logic board dying.
> 
The risk isn't as much both drives dying at the same time as one dying
during a rebuild of the array, which is more and more likely as drives
get bigger and bigger.