On Wed, 2011-03-30 at 07:58 +0200, Hannes Reinecke wrote: > On 03/30/2011 01:09 AM, Shyam_Iyer@xxxxxxxx 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. OK, I'll go for that ... Data Centre Bridging; experiences, technologies and needs ... something like that. What about virtualisation and open vSwitch? James -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
