AW: AW: [linux-lvm] SAN setup with host mirrored disks

[Kelly Sauke]

Fiederling, Daniel wrote:
> Currently I have only one path to each disk but further on I'd like to test a setup with multiple paths. But am I right that I have to use md on top of multipathd for getting the two disks mirrored?
>   
Yes, multipathd only handles the multiple paths on a per disk basis.  If 
you need them mirrored you have to use something on top of the multipath 
layer.  Using md is one option that should work just fine. 

> I tested different qla2xxx drivers (SuSE shipped, origanal download packages from qlogic, packages from hp) and the non suse offered much more module parameters - one of them was about en-/disabling failover. I would guess that the qla2xxx driver or the card firmware can handle multiple paths. But I'm not sure about that...
>
>
>   
I've yet to meet an HBA that doesn't work with multiple paths.   I would 
check EMC's support matrix for your particular card.  I know that we 
have to run specific EMC firmware on our HBAs to be fully supported.  I 
think by running the non EMC firmware you lose some of the functionality 
and may run into some stability issues.  I can't comment on that further 
since we've never done any testing with non-EMC firmware.

> -----Ursprüngliche Nachricht-----
> Von: linux-lvm-bounces at redhat.com [mailto:linux-lvm-bounces at redhat.com] Im Auftrag von Kelly Sauke
> Gesendet: Montag, 17. Juli 2006 15:36
> An: LVM general discussion and development
> Betreff: Re: AW: [linux-lvm] SAN setup with host mirrored disks
>
>   
>> Why do I have to expect io errors when using md? What is special about the Clariion setup? I would expect that the san disks are only "normal" scsi disks for linux...
>>   
>>     
> The difference comes in how the multiple paths to the same disk are 
> handled under linux.  If you only have one path to each disk, then this 
> doesn't apply to you. I guess I forgot to clarify if you had more than 
> one path.   Anyway, if you have multiple paths mpio knows which is the 
> Active path and which is the Passive path.  Sending IO down a passive 
> path will result in IO errors.
>
>
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