hdisk & hdiskpower

I am going to use EMC disks for AIX systems.    What do hdisk and hdiskpower represent?
IN AIX, we just say hdisk, but with EMC, we have hdisk and hdiskpower.  

thx much
ethanjohnsonsAsked:
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sentnerCommented:
hdiskpower is the powerpath device.  Basically it's a virtual device that balances the load across all of the assigned HBAs for that physical device, and provides path failure protection.  You want to use the hdiskpower devices instead of the hdisk devices because otherwise if an HBA went offline, you'd lose access to the devices on that path.  

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ethanjohnsonsAuthor Commented:
OK..  When you add PVs to VGs, do you add hdisks or hdiskpowers?  

The reason I am asking is that i.e. hdiskpower1 for hdisk50 and hdisk5.  I assume that you need to hdisks to VGs.

thx much

Pseudo name=hdiskpower1
Symmetrix ID=xxxxxxxxxxx
Logical device ID=020C
state=alive; policy=SymmOpt; priority=0; queued-IOs=0
==============================================================================
---------------- Host ---------------   - Stor -   -- I/O Path -  -- Stats ---
###  HW Path                I/O Paths    Interf.   Mode    State  Q-IOs Errors
==============================================================================
   1 fscsi1                    hdisk50   FA 10cB   active  alive      0      0
   0 fscsi0                    hdisk5    FA  7cB   active  alive      0      0
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sentnerCommented:
You should use the hdiskpower devices, otherwise you'll have problems if one path goes down.  
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