Re: Fibre Channel Shared Raid 5

On Monday August 29, neilb@cse.unsw.edu.au wrote:

On Sunday August 28, tlg1466@neo.tamu.edu wrote:

quoted

I recently stumbled upon ddraid.  Would this work at all for what I'm 
looking for?

I'm not certain, but I suspect not.

Having reflected a bit more on what I learned at the linux.conf.au
talk on the subject, I'm beginning to suspect "so" rather than "not".

ddraid uses a modified raid3 algorithm.
Each device block (which is typically 1 or 4 k) is split into
individual (512byte) sectors and these striped over the physical devices.
Thus every write is a full-stripe-write so no pre-reading is needed
and there is no need for co-ordination with other blocks to calculate
the parity.

Because if this, multiple hosts could write to the array providing
they agree beforehand who is allowed to write to which block - no
further co-ordination is required.

This co-ordination would be needed for dlvm or gfs anyway, so it is
quite possible that it can be used in a very distributed way.

However I've never actually used it, so I cannot promise anything.

NeilBrown