Re: ASM and EMC PowerPath

  • From: "Radoulov, Dimitre" <cichomitiko@xxxxxxxxx>
  • To: Karl Arao <karlarao@xxxxxxxxx>
  • Date: Mon, 11 Apr 2011 10:03:13 +0200


Karl,
thank you for clarifying,
>> "Unlike most multipath drivers, PowerPath will support full multipath capabilites 
>> even with the regular names.
>> PowerPath and ASMLib now work together successfully."
So it seems that we don't need to set any oracleasm variables with kernel 2.6 
(if I'm reading the note correctly) and multipathing will be used anyway,
the path used (regular or multi) is irrelevant, as far as ASM Lib is concerned. 


So in our case, EMC Powerpath, no scanorder or scanexclude,
we just need to configure the new disks with Powerpath
and create them with oracleasm using one of the available paths
(regular or multi, the choice is irrelevant).


Is this right or I'm missing something again?



Best regards
Dimitre


On 10/04/2011 22:30, Karl Arao wrote:

Hi Dimitre,

See my answers below..
1) but in order to actually use the multipath, you need to configure it correctly (check MOS Note 394956.1). 

    ANSWER: Also see the following notes
    - Configuring Oracle ASMLib on Multipath Disks [ID 309815.1]
    "Unlike most multipath drivers, PowerPath will support full
    multipath capabilites even with the regular names. PowerPath and
    ASMLib now work together successfully."
    - ORA-15072 when creating a diskgroup with external redundancy [ID
    396015.1] which pertains to the "Linux multipath" and not the "EMC
    Powerpath"
2) if on reboot (or after scandisk) asmlib chooses a path different than the multipath and the chosen path becomes unavailable, you won't be able to access those disks 
no more (you'll get errors)

    ANSWER:
    - it will not choose a path other than the configured EMC
    Powerdevice if you have properly configured the persistent
    binding... so you must ensure that the storage engineer have
    properly configured the "multipathing" and "persistent binding"
3) If you configure the access to the disks with asmlib (via scanorder or scanexclude) through the multipath, the disks will remain accessesible even if you loose one or more of the paths to those disks (assuming at least one path is still available). 

    ANSWER:
    - again.. "Unlike most multipath drivers, PowerPath will support
    full multipath capabilites even with the regular names. PowerPath
    and ASMLib now work together successfully."
The only error so far that I've seen on EMC multipathing is this.. which you can ignore as per powerlink http://karlarao.tiddlyspot.com/#[[Buffer%20IO%20error]] and the only time I have to exclude powerdevices is when I have to configure it for LVM ... http://karlarao.tiddlyspot.com/#EMCPowerDevicesOnLVM 


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Karl Arao
karlarao.wordpress.com <http://karlarao.wordpress.com>
karlarao.tiddlyspot.com <http://karlarao.tiddlyspot.com>


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