Plans for BTRFS in Fedora

Milan Broz mbroz at
Wed Feb 23 23:26:31 UTC 2011

On 02/23/2011 07:41 PM, Peter Jones wrote:
> On 02/23/2011 12:50 PM, Lars Seipel wrote:

>> If you want to stack it on top of dm-crypt there are caveats as well.
> Right, which is what we'd wind up doing in the encrypted case.
>>> From btrfs-wiki:
>>> btrfs volumes on top of dm-crypt block devices (and possibly LVM) require
>>> write-caching to be turned off on the underlying HDD. Failing to do so, in
>>> the event of a power failure, may result in corruption not yet handled by
>>> btrfs code. (2.6.33)

This is completely nonsense and FUD. We asked several times for reproducer
and nobody from btrfs camp was able to provide one. 

If you have reproducer, please send it to me and I'll fix dmcrypt code.
But I am almost sure there is no such problem in current code.

> So, don't hold me to this, but it looks as if the normal lvm behaviour was
> fixed at least as of d87f4c14f2 .  That being said, dm-crypt still just throws
> REQ_FLUSH away instead of figuring out the block remaps involved and issuing
> the right bios. Of course, this is a problem with dm-crypt and _any_ filesystem.

Another nonsense. See 2.6.37 source code, REQ_FLUSH is processed by dm-crypt
correctly. It supported even barriers some time before (at least in 2.6.36).

Anything else for today?


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