[Linux-cluster] Re: [ddraid] extensibility

Jakob Praher jpraher at yahoo.de
Wed May 11 18:38:58 UTC 2005

sorry, I meant daniel and all that are working with/on ddraid,

Jakob Praher wrote:
> I am very interested in ddraid for having sios systems over the network.
> A few questions though:
> I've looked shortly at your implementation (ddraid-0.5.0), but have a
> few questions, which I thought to ask you:
> * how will you track extensibilty:
> afaik you assign a fixed number of logical sectors to the device mapper
>  device. but lets take a trivial example:
> you have 3 disks (2^k+1), each in a sperate computer.
> then you want to plug a 4th and 5th disk (2^k+1) disk (again separate
> computer) in the ddraid - how should that look like regarding the dm setup?
> what problems could arise given the striping information on the blocks.
> do you simply extend a stripe from 2 to 4 data blocks? is it possible to
> raise the number of logical sectors with device mapper (sorry for my
> ignorance - I haven't looked the details of the dmsetup man page). do
> you have to rearrange block sizes or stripe information?
> * have you investigated raid-x - would that be possible to implement via
> device mapper?
> I've looked closer on a the papers by hwang et al regarding Raid-x,
> which also provides a single io space for servlerless clusters. The
> design is basically a mixture of mirroring and striping, making it
> possible for one node to fail completly.
> On stripe is made of (n-1) blocks and you have (n-1) mirror blocks. They
> have implemented as part of their trojan cluster project, wich I think
> isn't alive any more.
> I look forward to hearing from you.
> -- Jakob

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