Re: Device-mapper target driver for Write tracking

[Daniel Armbruster <dani.armbruster@gmx.de>]

On 13:43 Wed 19 Oct     , Zdenek Kabelac wrote:
> Dne 19.10.2016 v 12:53 Daniel Armbruster napsal(a):
> > Hi List,
> >
> > I'm looking for a device-mapper target driver giving me the possibility to
> > track/log WRITE requests. The idea is to track those WRITE requests within a
> > Bitmap e.g. 1:LV-EXTEND (for LVM2). I read already the device-mapper
> > documentation under
> >
> > https://www.kernel.org/doc/Documentation/device-mapper/
> >
> > but didn't find an appropriate module which would suite my needs.
> >
> > Is there any work happening on this to leverage? Any kind of help is
> > appreciated.
> >
> > Many thanks in advance.
> 
> 
> Hi
> 
> 
> Not exactly sure what you are trying to do but 2 things to look at:
> 
> Maybe  'dmstats' with it's region logic may cover your 'wanted' operation.
> 
> The kernel dm target to check would be  'era' which keeps trace
> of written blocks.
> 
> Regards
> 
> Zdenek
> 
> 
> 
Hi Zdenek,

thanks for your help.

I'm trying to implement a synchronization tool which performs backups in an
intelligent way. Since using a snapshot is only partly an option (the snapshot
could fill up and the snapshot_autoextend_* practicality of LVM2 isn't stable
enough under heavy load) I was thinking about the possibility of an additional
device which keeps trace of written blocks. To improve performance I aim at
reducing the data throughput. That's why I was thinking about a Bitmap e.g.
1:LV-EXTEND.

I thought already about the DM statistics module. Is there any performance
impact when collecting statistics for a given volume (except of the
additionally allocated memory used)? Is there a possibility to quantify it?

As well I'm going to have a closer look at the era module. Many thanks for the
hint.

Regards,
Daniel


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