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Re: [dm-devel] change tracking with block-level granularity using md

On 12/18/2013 09:04 AM, Thomas Knauth wrote:
> Hello list,
> I am the author of the following paper
> https://www.usenix.org/conference/lisa13/technical-sessions/papers/knauth
> just presented at LISA 2013. Folks at the conference expressed
> interested in seeing this merged into the official Linux kernel. I
> would like to gauge your opinion of whether this has a chance to
> actually be accepted.
Well, you just implemented an asynchronous mirror with discrete
tools. Congratulations.
Using bitmaps for tracking modified blocks has been a standard
technique in RAID1 for ages.

(look for mdadm --write-behind and drivers/md/bitmap.c. It's not
actually _new_ ...)

Sorry for being sarcastic.

But nevertheless, your tool might actually be useful; tracking block
changes could have some benefit on other areas.

What you should be doing:
- Rename the thing (dm-linear is taken; maybe dm-bitmap ?)
- Use debugfs instead of /proc
- Proper formatting

And then send the code for review.

Or go for the full monty and break up dm-mirror to include your
bitmap code. But then you would need to come up with a way of
storing your bitmap on disk.
Which is where the _real_ fun starts.


Dr. Hannes Reinecke		      zSeries & Storage
hare suse de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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