Re: device delete, error removing device

[Goffredo Baroncelli <kreijack@gmail.com>]

On 2012-10-22 21:50, Hugo Mills wrote:
>>>>> It's more like a balance which moves everything that has
>>>>> some (part of its) existence on a device. So when you have
>>>>> RAID-0 or RAID-1 data, all of the related chunks on other
>>>>> disks get moved too (so in RAID-1, it's the mirror chunk as
>>>>> well as the chunk on the removed disk that gets
>>>>> rewritten).
>>> 
>>> Does this mean "device delete" depends on an ability to make
>>> writes to the device being removed? I immediately think of SSD
>>> failures, which seem to fail writing, while still being able to
>>> reliably read. Would that behavior inhibit the ability to
>>> remove the device from the volume?
> No, the device being removed isn't modified at all. (Which causes 
> its own set of weird problemettes, but I think most of those have
> gone away).

IIRC, when a device is deleted, the 1st superblock is zeroed.
Moreover btrfs needs to be able to read the device in order to delete
it. Of course these rules aren't applied when a device is classified
as "missing".

See the function btrfs_rm_device() in fs/btrfs/volumes.c for the details.

> 


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