Re: Re: device mapper integrated loops - and one more year !

["Bryn M. Reeves" <breeves@redhat.com>]

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devzero@web.de wrote:
> Hello !
> 
> after desparately seeking for a solution to have more than 256 loop
> devices (for a huge cd-rom server), i have recently come across
> dm-loop, which looks very promising (to replace loop.c)
> 
> can i have more than 256 devices which this?

Hi Roland,

Yes, dm-loop will support as many loop devices as device-mapper can allow.

> our cd-rom server is going to have more than 256 iso-images soon and
> i need to upgrade to a more recent OS, anyway, so this won`t be a 
> problem that dm-loop is so brand new.
> 
> but - any timeline for dm-loop mainline inclusion ?
> 
> should i wait for 2.6.19 or 2.6.20 ?

There isn't a fixed timeline. We are currently working to improve the
lookup code - the prototype patch uses a linear search which doesn't
scale well for large/fragmented image files. I have some tests running
at the moment and we hope to have something soon - the results so far
are good, it's just a case of selecting between a couple of different
methods.

The changes dm-loop requires in device-mapper core are pretty minor and
have already been merged in 2.6.19, so it's just the dm-loop patch
itself remaining.

> is it already useable with less recent kernels, i.e. can i download
> dm-loop patch and recent dmsetup tool and use with older kernel ?

This should work fine - there are a couple of known issues with the
existing patch, but unless you are using large images (>2G), or have a
severely fragmented filesystem you shouldn't run into these.

I'll see if we can get a revised version of the current patch for wider
testing in the next couple of weeks - let me know if you would be
interested in trying this out.

Thanks,

Bryn.
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