RE: [dm-devel] multipath and san fabric

[Edward Goggin <egoggin emc com>]

You may want to also cross connect across the 2 target
controllers (A,B) in case 2.  Doing so provides more
redundancy for asymmetric arrays and better resource
utilization in case of a failure of either an HBA or
target controller which would otherwise prevent
utilization of the other HBA or target controller
for that LU when load sharing I/O across multiple
paths.

So the I_T nexus's for the 4 paths are:

	HBA1_TargetPort1
	HBA1_TargetPort3
	HBA2_TargetPort2
	HBA2_TargetPort4

> -----Original Message-----
> From: dm-devel-bounces redhat com 
> [mailto:dm-devel-bounces redhat com] On Behalf Of James Smart
> Sent: Monday, November 13, 2006 2:18 PM
> To: jslittl hendricks org; device-mapper development
> Subject: Re: [dm-devel] multipath and san fabric
> 
> If the hba's are on different fabrics - why would you ever put an hba
> that is not in the fabric in a zone in that fabric ?  (e.g. 
> your second
> option makes no sense).
> 
> If you are stating that the 2hba's are on different fabrics 
> (and in zones
> within those fabric) - but they are seeing the same Storage 
> device on both
> fabrics - then the dm config (note: I'm not talking about 
> zoning anymore)
> would have a path per I_T nexus. I state it this way to 
> account for dual-ported
> controllers, which may appear as separate targets, may exist 
> within the fabric.
> 
> Example 1:
>    Fabric A contains HBA1 and TargetPort1. Typically a zone 
> would exist
>      within Fabric A that contains these 2 ports.
>    Fabric B contains HBA2 and TargetPort2. Typically a zone 
> would exist
>      within Fabric B that contains these 2 ports.
>    The storage array contains 2 controllers with 1 port per 
> controller, or
>      is a single controller with 2 ports. Either way, the two 
> ports are
>      TargetPort1 and TargetPort2, are on the same array, and 
> all storage
>      can be seen from any port.
>    --
>    This would have 2 DM paths.
>    The I_T nexus's are:
>       HBA1_TargetPort1
>       HBA2_TargetPort2
> 
> Example 2:
>    Fabric A contains HBA1, TargetPort1, and TargetPort3. 
> Typically a zone
>      would exist within Fabric A that contains these 3 ports.
>    Fabric B contains HBA2, TargetPort2, and TargetPort4. 
> Typically a zone
>      would exist within Fabric B that contains these 3 ports.
>    The storage array contains 2 controllers, with 2 ports per 
> controller.
>      Meaning TargetPort1 and TargetPort2 are on controller A, 
> and TargetPort3
>      and TargetPort4 are on controller B. The ports are cross 
> connected on
>      the fabrics for redundancy. All storage can be seen from 
> any port.
>    --
>    This would ahve 4 DM paths
>    The I_T nexus's are:
>       HBA1_TargetPort1
>       HBA1_TargetPort2
>       HBA2_TargetPort3
>       HBA2_TargetPort4
> 
> -- james
> 
> John Little wrote:
> > Hi all
> > 
> > Admittedly this is not the correct forum for this question 
> but I have googled 
> > this and the only people I have to ask around here are 
> people who won't touch 
> > it because it is Linux.
> > 
> > My question is this:  I'm using SLES10 with two emulex 
> hbas, one connected to 
> > fabric a and one to fabric b.  When zoning the switch for 
> the hbas do I put 
> > in only one path to the fabric per hba or do I put in two, 
> one to each of the 
> > separate fabrics?
> > 
> > Again I realize this is not exactly the correct forum but 
> since I couldn't 
> > find an answer anywhere else I figured you guys would be the most 
> > knowledgeable.  If there are some docs somewhere that you 
> could point me to I 
> > would appreciate it.
> > 
> > John
> > 
> > --
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> > dm-devel redhat com
> > https://www.redhat.com/mailman/listinfo/dm-devel
> > 
> 
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