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RE: Qlogic FC Multipath and engenio

> -----Mensaje original-----
> De: Andrew Miehs [mailto:andrew@2sheds.de]
> Enviado el: Miércoles, 01 de Febrero de 2006 08:53 a.m.
> Para: Doug Griswold
> CC: debian debian-isp
> Asunto: Re: Qlogic FC Multipath and engenio
> Setup is as follows
>   * 1 port on Server HBA connected to a switch
>   * port 1 from controller A on D240 connected to switch
>   * port 1 from controller B on D240 connected to switch
>   * LUN1 (disk) default active over controllerA
>   * LUN2 (disk) default active over controllerB
> What confuses me is NOT that fact that I see both disks twice, (so  
> four devices in total)
> sdc, sdc, sdd, sde BUT that I can only access two of these - via the  
> 'active'
> controller on the storage system.

Some SAN solutions do not support Active-Active redundancy where both
controllers are active at the same time. For example en HP EVA3000 the
the controllers implement an Active-Passive redundancy; for each
vdisk created in the SAN there is only one active controller that accepts
commands for the disk. Whereas HP EVA6000 or HP EVA8000 implement
active-active redundancy and you can use native Multi-Path I/O drivers
of Solaris, AIX, Linux to implement redundancy. 
> If I access the 'second path' via the 'other' controller to a 
> disk, I  
> get io errors...

If active-active redundancy is not implemented, access to a vdisk 
through the passive controller results in timeout and I/O errors.

> Is this normal? I was expecting that all controllers offer all disks  
> equally, and am
> a bit confused about this 'default active' setting...
> I has hoping to avoid compiling the RDAC driver from engenio 
> as it is  
> 'configured'
> for RedHat or Suse, and I now have to go through the Makefile to fix  
> it - hopefully
> this should be pretty easy... Their RDAC driver seems to use 'MPP'  
> for the failover

Some vendor drivers implement vendor-specific controller switch-over
code. For example, vendor Qlogic drivers for Linux permit redundant 
I/O paths and transparent switch-over to the standby controller even
with HP EVA3000, while in Solaris MPIO with active-passive redundancy
does not work and the HP Secure Path software is requiered for
implementing a fault tolerant solution.

PS: Company policy forces me to use Outlook for e-mail. Sorry for
dumb formatting...


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