[dm-devel] Possible bug in mirror target

[Zdenek Kabelac]

Dne 13. 02. 19 v 16:01 Bryn M. Reeves napsal(a):
> On Wed, Feb 13, 2019 at 03:21:52PM +0100, Zdenek Kabelac wrote:
>> If you have this free space it's surely not a bad thing - but there
>> are many cases, you can get any free space - majority of filesystems
>> does not support shrinking - so the only 'free' space you can
>> get is by adding new storage to VG - again quite limiting factor.
> 
> Probably obvious to many, but if you find yourself in this situation
> using the Red Hat / Fedora default layout created by Anaconda, the
> easiest solution is normally to "steal" one extent from the auto-
> configured swap LV, and donate it to the mirror conversion:
> 
>    # swapoff -a
>    # lvresize -l -1 rhel/swap
>    # mkswap /dev/rhel/swap
>    # swapon -a
>    # lvchange -m1 ...
> 
> This will always work with the automatic layouts provided by those
> distros.

Just to further clear this - yeah - stealing 1 extent this way 'mostly' 
temporarily works, however for conversion to 'raid' - the rule should be, that 
log/metadata device for each leg should be co-located on the same physical 
device as the leg itself - clearly storing multiple or all metadata devices on 
1 physical device will not have required purpose - although as long as all 
devices do run correctly such setup will appear as usable (and user will 
actually not get any warning that setup is actually not very safe for device 
failure)

Regards,
Zdenek