James Pearson
2009-Mar-13 15:36 UTC
[CentOS] Help setting up multipathing on CentOS 4.7 to an Equallogic iSCSI target
I'm trying to test out an Equallogic PS5500 with a server running CentOS 4.7 I can create a volume and mount it fine using the standard iscsi-initiator-utils tools. The Equallogic box has 3 Gigabit interfaces and I would like to try to set up things so I can read/write from/to the volume using multiple NICs on the server i.e. get 200+ Mbyte/s access to the volume - I've had some basic info from Equallogic (Dell) saying that I need to set up DM multipathing - however, the info I have starts by saying that I have to: "Make sure the host can see multiple devices representing the same target volume" However, I'm not sure how I get to this point i.e. how do I set up the Equallogic and/or server so that I can see a single volume over multiple network links? Has anyone set up one of these Equallogic boxes in this way using CentOS4/RHEL4 ? Thanks James Pearson
George Negoita
2009-Mar-13 16:28 UTC
[CentOS] Help setting up multipathing on CentOS 4.7 to an Equallogic iSCSI target
Hello, On Fri, Mar 13, 2009 at 5:36 PM, James Pearson <james-p at moving-picture.com> wrote:> I'm trying to test out an Equallogic PS5500 with a server running CentOS 4.7Try reading this: http://linfrastructure.blogspot.com/2008/02/multipath-and-equallogic-iscsi.html http://lists.centos.org/pipermail/centos/2008-June/059358.html http://www.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5.2/html/DM_Multipath/index.html http://kbase.redhat.com/faq/docs/DOC-2877 This is what helped me understand how to setup dm-multipath on centos 5 using iet iscsi target. -- George Negoita System Administrator iMedia Plus Group
nate
2009-Mar-13 16:49 UTC
[CentOS] Help setting up multipathing on CentOS 4.7 to an Equallogic iSCSI target
James Pearson wrote:> I'm trying to test out an Equallogic PS5500 with a server running CentOS 4.7 > > I can create a volume and mount it fine using the standard > iscsi-initiator-utils tools. > > The Equallogic box has 3 Gigabit interfaces and I would like to try to > set up things so I can read/write from/to the volume using multiple NICs > on the server i.e. get 200+ Mbyte/s access to the volume - I've had some > basic info from Equallogic (Dell) saying that I need to set up DM > multipathing - however, the info I have starts by saying that I have to: > > "Make sure the host can see multiple devices representing the same > target volume" > > However, I'm not sure how I get to this point i.e. how do I set up the > Equallogic and/or server so that I can see a single volume over multiple > network links?Dell should be able to tell you this. If you want 2Gbit+/sec throughput what you should probably be looking at instead of multipathing is something like 802.3ad, if the equalogic box has different IPs on each interface you will be able to get up to 3Gbit/s of throughput and still have fault tolerance and not have to mess with multipathing(assuming the equalogic box does IP takeover when one of the interfaces goes down). Now I have a hard time believing that the software iscsi client in linux can handle that much throughput but maybe it can, I'd put money down that you'd be looking at a pretty good chunk of your CPU time being spent on that though. And of course use jumbo frames, and have a dedicated network for storage(at least dedicated VLANs), and dedicated NICs. Last I heard equallogic didn't support anything other than jumbo frames so you should have that setup already. multipathing is more for storage systems that have multiple controllers and detecting when one of those controllers is not accessible and failing over to it. While you may be able to come up with a multipathing config with device mapper that has different volumes being presented down different paths thus aggregating the total throughput of the system(to the different volumes), I'm not aware of a way myself to aggregate paths in device mapper to a single volume. For my storage array I use device mapper with round robin multipathing which alternates between however many I/O paths I have(typically there are 4 paths per volume), however at any given moment for any given volume only 1 path is used. This can only be used on arrays that are truely "active-active", do not attempt this on an active-passive system or you'll run into a heap of trouble. I haven't used equallogic stuff before but if they have IP takeover for downed interfaces/controllers than your best bet is likely handling link aggregation/failover at the network level, move the controller failover entirely to the equalogic system, instead of trying to track it at the server level(of course with 802.3ad you will be tracking local network link status at the server level). My storage vendor gave explicit step by step instructions(PDF) as to what was needed to setup device mapper to work properly with their systems. Given Dell is a big company too, I'd expect you to easily be able to get that information from them as well. While most of the connectivity on my storage array is Fiber, there are 4x1Gbps iSCSI ports on it, however the ports are not aggregated, so the most any single system can pull from the array at a time is 1Gbps (despite there being 4x1Gbps ports, two on each HBA, there is actually only 1Gbps of throughput available on each HBA, so in essence there are 2x1Gbps ports available). In aggregate though, with multiple systems hitting the array simultaneously you can drive more throughput. That is assuming you still want to go the device mapper route. nate