warnings for silly/pointless raid levels

warnings for silly/pointless raid levels

[sam tygier]

Hi,
I recently got into a stick situation because i had a btrfs volume with data in raid1 but metadata as dup. when i removed one of the drives i could not mount as degraded. This was my error as i did not convert the metadata when i converted it from a single/dup volume.

But i wonder if there should be a warning for raid combinations that are probably mistakes. raid1/dup, provides no protection against a failed disk, but uses as much space as if it did. so maybe the tools could have refused to allow it without a --force. 

sam

Re: warnings for silly/pointless raid levels

[Chris Murphy]

On Oct 28, 2012, at 4:20 PM, sam tygier <samtygier@yahoo.co.uk> wrote:

> Hi,
> I recently got into a stick situation because i had a btrfs volume with data in raid1 but metadata as dup. when i removed one of the drives i could not mount as degraded. This was my error as i did not convert the metadata when i converted it from a single/dup volume.
> 
> But i wonder if there should be a warning for raid combinations that are probably mistakes. raid1/dup, provides no protection against a failed disk, but uses as much space as if it did. so maybe the tools could have refused to allow it without a --force.

I think the argument I've read recently, is that an automatic "upgrade" of metadata to raid1 in this case is desired. I'd like to see metadata upgraded to raid1 when a 2nd disk is added in any case, by default. In data raid0 or single, I'm probably hosed with one drive failures, but maybe I can get some fragments off the drive if I have metadata. Is there a downside? I don't think so because the default metadata profile for multiple device mkfs is raid1 in any case.


Chris Murphy