[dm-devel] [Lsf] Preliminary Agenda and Activities for LSF

[Hannes Reinecke]

On 03/30/2011 01:09 AM, Shyam_Iyer at dell.com wrote:
>
> Let me back up here.. this has to be thought in not only the traditional Ethernet
 > sense but also in a Data Centre Bridged environment. I shouldn't 
have wandered
 > into the multipath constructs..
>
> I think the statement on not going to the same LUN was a little erroneous. I meant
 > different /dev/sdXs.. and hence different block I/O queues.
>
> Each I/O queue could be thought of as a bandwidth queue class being serviced through
 > a corresponding network adapter's queue(assuming a multiqueue 
capable adapter)
>
> Let us say /dev/sda(Through eth0) and /dev/sdb(eth1) are a cgroup bandwidth group
 > corresponding to a weightage of 20% of the I/O bandwidth the user 
has configured
 > this weight thinking that this will correspond to say 200Mb of 
bandwidth.
>
> Let us say the network bandwidth on the corresponding network queues corresponding
 > was reduced by the DCB capable switch...
> We still need an SLA of 200Mb of I/O bandwidth but the underlying dynamics have changed.
>
> In such a scenario the option is to move I/O to a different bandwidth priority queue
 > in the network adapter. This could be moving I/O to a new network 
queue in eth0 or
 > another queue in eth1 ..
>
> This requires mapping the block queue to the new network queue.
>
> One way of solving this is what is getting into the open-iscsi world i.e. creating
 > a session tagged to the relevant DCB priority and thus the 
session gets mapped
 > to the relevant tc queue which ultimately maps to one of the 
network adapters multiqueue..
>
> But when multipath fails over to the different session path then the DCB bandwidth
 > priority will not move with it..
>
> Ok one could argue that is a user mistake to have configured bandwidth priorities
 > differently but it may so happen that the bandwidth priority was 
just dynamically
 > changed by the switch for the particular queue.
>
> Although I gave an example of a DCB environment but we could definitely look at
 > doing a 1:n map of block queues to network adapter queues for 
non-DCB environments too..
>
That sounds quite convoluted enough to warrant it's own slot :-)

No, seriously. I think it would be good to have a separate slot 
discussing DCB (be it FCoE or iSCSI) and cgroups.
And how to best align these things.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare at suse.de			      +49 911 74053 688
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