Open Stack

Is Swift as a Block device a real option? It looks to me that
performance will be a big problem. Also how the three copies of Swift
will be presented as iSCSI?  Only one? Each one with its own iSCSI
target? Who serialize the writes in this scenario?

Nelson

On Mon, May 2, 2011 at 6:11 PM, Eric Windisch <eric at cloudscaling.com> wrote:
>
>> Surely, FUSE is another possible option, I think. I heard that lunr
>> team was thinking about the approach too.
>
> I'm concerned about the performance/stability of FUSE, but I'm not sure if using iSCSI is a significantly better option when the access is likely to be local. If I had to choose something in-between, I'd evaluate if NBD was any better of a solution.
>
> I expect there will be great demand for an implementation of a Swift as a block device client.  Care should be made in deciding what will be the best-supported method/implementation. That said, you have an implementation, and that goes a long way versus the alternatives which don't currently exist.
>
>
>> As I wrote in the previous mail, the tricky part of the dm-snapshot
>> approach is getting the delta of snaphosts (I assume that we want to
>> store only deltas on Swift). dm-snapshot doesn't provide the
>> user-space API to get the deltas. So Lunr needs to access to
>> dm-snapshot volume directly. It's sorta backdoor approach (getting the
>> information that Linux kernel doesn't provide to user space). As a
>> Linux kernel developer, I would like to shout at people who do such :)
>
>
> With dm-snapshot, the solution is to look at the device mapper table (via the device mapper API) and access the backend volume. I don't see why this is a bad solution. In fact, considering that the device mapper table could be arbitrarily complex and some backend volumes might be entirely virtual, i.e. dm-zero, this seems fairly reasonable to me.
>
> I really don't see at all how Swift-as-block-device relates at all to (storage) snapshots, other than the fact that this makes it possible to use Swift with dm-snapshot.
>
> Regards,
> Eric Windisch
> eric at cloudscaling.com
>
>
>
>
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