Re: bcache and LVM

[Nikolaus Rath <Nikolaus@rath.org>]

On Feb 09 2016, "Jens-U. Mozdzen" <jmozdzen@nde.ag> wrote:
> Hi Nikolaus,
>
> Zitat von Nikolaus Rath <Nikolaus@rath.org>:
>> On Feb 08 2016, "Jens-U. Mozdzen" <jmozdzen@nde.ag> wrote:
>>> [...]
>>> The article itself does positively mention sub-dividing bcache devices
>>> using LVM.
>>
>> Yep, but the talk page then says:
>>
>> | Initially, LVM did not recognize my /dev/bcache0 when I wanted to
>> | create a physical volume on it. For anyone else who has that issue,
>> | this may be relevant:
>> | http://www.redhat.com/archives/linux-lvm/2012-March/msg00005.html.
>
> this still holds true even with LVM on OpenSUSE Leap 42.1 (which is
> what we're using ATM) - but that's no "stability issue", but rather an
> installation nuisance. You only need to tell LVM to consider bcache
> devices at all, by extending /etc/lvm/lvm.conf.

Indeed. But it's also yet another slightly worrying tidbit (maybe LVM is
not considering it by default for a good reason).

Also, just now someone on -btrfs advised:

| > Otherwise I'll give bcache a shot. I've avoided it so far because of the
| > need to reformat and because of rumours that it doesn't work well with
| > LVM or BTRFS. But it sounds as if that's not the case..
|
| It should work fine with _just_ BTRFS, but don't put any other layers
| into the storage system like LVM or dmcrypt or mdraid, it's got some
| pretty pathological interactions with the device mapper and md
| frameworks still.


Best,
-Nikolaus

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