[dm-devel] write directly to device mapper snapshot origin device ?

[Mikulas Patocka]

On Fri, 15 Jul 2016, Navin P.S wrote:

> Resend ..
> 
> On Thu, Jul 14, 2016 at 7:55 PM, Navin P.S <navinp1912 at gmail.com> wrote:
> > Hi,
> >   Can i do dd if=/dev/zero of=/dev/mapper/dmo count=20 ? where dmo is
> > a dm snapshot origin created through dmsetup command. Instead of
> > /dev/zero i can write valid devices.
> >
> > I could create the dmo through some lvm2 commands.

lvcreate -s

> > Is direct write
> > with 4k (page size values ) allowed when it is mapped to 2 block
> > devices in linear mode ?
> >
> >
> > Regards,
> > -- Navin
> 
> I'm seeing  OOM followed by reboot of host machine.
> Does this mean this device cannot to exported to containers for writing ?

The snapshot driver requires 32 bytes of memory for one chunk (the chunk 
size is selected with the "-c" switch to lvcreate). You should set system 
memory according to that.

Mikulas

> -- Navin
>