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San disk appearing double in old AIX


 
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Operating Systems AIX San disk appearing double in old AIX
# 8  
Old 08-06-2014
What will you do if the single FC card fails? You will lose your SAN connection, and may have a long wait for a replacement.
# 9  
Old 08-06-2014
Fibre channel storage uses a system of World Wide Names (WWN) to identify disks or other pieces of array. Some FC storage controllers allow you to assign (pseudo) WWN's to arrays created by the controller. Only one WWN should be allocated to any one piece of storage.

A modern host O/S storage driver will realize that when it can see the same WWN via different routes that it is actually the same storage that it can see through different routes and then manage that topology (by only using one route at a time unless the storage controller can accept MPIO, but also use an alternative route if the primary route fails).

Last edited by hicksd8; 08-07-2014 at 05:51 AM..
# 10  
Old 08-07-2014
Quote:
A modern host O/S storage driver will realize that when it can see the same WWN via different routes that it is actually the same storage that it can see through different routes and then manage that topology (by only using one route at a time, but also use an alternative route if the primary route fails).
Actually I want to do the behaviour of the modern driver with the old one.

If I allocated only one WWN for a LUN, then i have no secondary route in case of failure ?

Last edited by rbatte1; 08-11-2014 at 06:13 AM.. Reason: Added QUOTE tags and spelling/grammer
# 11  
Old 08-07-2014
Quote:
Originally Posted by Tharsan
Actually i want to do the behaviour of the modern driver with the old one.
You can't. You will have to install some sort of MPIO driver (which one that is depends on the SAN you use) and this driver will bundle several hdisk-devices (they represent the OSes view of the disk) to one multipath-device (vpath, powerpath, ..., these represent the multipath drivers view of the device)

Quote:
Originally Posted by Tharsan
If i allocated only one WWN for a LUN, then i have no secondary route in case of failure ?
See above, my rather exhaustive explanation of how a SAN works (#3): no! A WWN is like an address, not a way to get there. Regardless of the route you take it always ends at the same LUN. The WWN is an attribute of the LUN, not the path (otherwise all LUNS sharing the same path would have the same WWNs, no?)

I hope this helps.

bakunin
# 12  
Old 08-07-2014
thanks for yours replies !

I understand better now Smilie
# 13  
Old 08-11-2014
AIX 5.3 should support this with the correct driver.

Have a look at this and this as a starting point on the IBM website. Does that give you an option?


I still worry that if you have a card failure, you lose your disks, or if you have a port failure, it requires downtime to replace. There is likely some performance overhead too, but it depends how hard the IO is being driven.



Robin
# 14  
Old 08-11-2014
AIX only introduced support for the DS3400, with either native AIX MPIO or the (now obsolete) RDAC driver in AIX 5.3 TL06 so I'm afraid you are out of luck unless you update something.

Checkout the SSIC site for your available options, including the firmware release of the DS that is supported:
IBM System Storage Interoperation Center (SSIC)

Please also note that the DS3400 is only capable of active / passive control so all the multipath chat above doesn't really apply to your storage subsystem, each adapter should only be able to see one storage controller and as you have a direct connection - one fcs or fscsi device can only see one controller - your connections are fine.

HTH

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