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Full Discussion: Path missing???
Operating Systems AIX Path missing??? Post 302883449 by bakunin on Tuesday 14th of January 2014 08:54:43 AM
Old 01-14-2014
Quote:
Originally Posted by Thala
but why its getting 4paths for an Dual port adapter?
It has nothing to do with how many ports one adapter has. A "path" is just a way of looking at one disk. The short answer is, a "path" is a certain connection from the system to the disk, using a specific way.

Here is the long version: consider the following setup. You have one FC-Adapter (two ports, FCa, FCb), which is connected to two FC-switches (SWa, SWb), which both connect to a storage system. The switches are themselves connected via a crossover-link. You create a single disk on this storage system. This disk will be seen over different paths: FCa-SWa-Disk, FCa-SWa-SWb-Disk, FCb-SWb-Disk, FCb-SWb-SWa-Disk. AIX will therefore create 4 different hdisk-devices when you run cfgmgr.

Now, this is not very comfortable, especially when you create several disks. Each disk will be seen via 4 paths (if you have a fabric more complex than the one i sketched above you might have even more paths) and soon you will have trouble to remember that hdisk137 is in fact hdisk49 and also hdisk87 and hdisk3.

This is where MPIO comes into play: it takes all the hdisk-devices which represent in fact one and only one disk (its like taking a picture of a building from several angles - regardless of how many pictures you take it is always the same one building) and builds a "super-device" above them. You can use this super-device to build VGs, LVs and all other sorts of things you use normally disks for. The MPIO (Multipath-I/O) driver will take care about the relationship of the different hdisk devices and do the bookkeeping for you (and the OS as well).

And there is an additional advantage to it: suppose Switch A in the above picture would fail. Two of the four hdisks (the two paths involving SWa) would be inaccessible, because these pathes would not be usable, but the super-device still works, because it uses ALL paths and if two fail there are still two more to use. In fact this is the main reason one builds such complex fabrics with parallel FC-switches, crossover-links and the like.

I hope this helps.

bakunin
 

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LEARN ABOUT SUNOS

scf_card_reset

SCF_Card_reset(3SMARTCARD)				    Smartcard Library Functions 				SCF_Card_reset(3SMARTCARD)

NAME

       SCF_Card_reset - perform a reset of a smartcard

SYNOPSIS

       cc [ flag... ] file... -lsmartcard [ library...]
       #include <smartcard/scf.h>

       SCF_Status_t SCF_Card_reset(SCF_Card_t card);

PARAMETERS

       card	       The card (from SCF_Terminal_getCard(3SMARTCARD)) to be reset

DESCRIPTION

       The SCF_Card_reset() function causes the specified smartcard to be reset by the terminal.

       A  card	can  be  reset only if it has not been locked (with SCF_Card_lock(3SMARTCARD)) by another client. A client wishing to reset a card
       should either first call SCF_Card_lock() to obtain the card lock, or be prepared to retry the reset operation if it fails  because  another
       client holds the card lock.

       When  the  card is reset, any SCF_Card_t object representing the card will continue to remain valid after the reset. When the reset occurs,
       an SCF_EVENT_CARDRESET event will be sent to all registered event listeners for the terminal (assuming they  registered	for  this  event).
       This  is the only notification of a reset provided to SCF clients. When a client receives this event, it should be prepared to reinitialize
       any state on the card that might have been interrupted by the reset. New information about the card (for example, ATR, if it  changed)  can
       also be available from SCF_Card_getInfo(3SMARTCARD).

RETURN VALUES

       If  the	card is successfully reset, SCF_STATUS_SUCCESS is returned. Otherwise, the status of the card remains unchanged and an error value
       is returned.

ERRORS

       The SCF_Card_reset() function will fail if:

       SCF_STATUS_BADHANDLE    The specified card has been closed or is invalid.

       SCF_STATUS_CARDLOCKED   The card cannot be reset because another client holds a lock on the card.

       SCF_STATUS_CARDREMOVED  The card cannot be reset because the card represented by the SCF_Card_t has been removed.

       SCF_STATUS_COMMERROR    The connection to the server was lost.

       SCF_STATUS_FAILED       An internal error occured.

EXAMPLES

       Example 1: Reset a card.

       SCF_Status_t status;
       SCF_Card_t myCard;

       /* (...call SCF_Terminal_getCard to open myCard...) */

       status = SCF_Card_lock(myCard, SCF_TIMEOUT_MAX);
       if (status != SCF_STATUS_SUCCESS) exit(1);

       status = SCF_Card_reset(myCard);
       if (status != SCF_STATUS_SUCCESS) exit(1);

       status = SCF_Card_unlock(myCard);
       if (status != SCF_STATUS_SUCCESS) exit(1);

       /* ... */

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Evolving			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       libsmartcard(3LIB), SCF_Card_getInfo(3SMARTCARD), SCF_Card_lock(3SMARTCARD),  SCF_Terminal_addEventListener(3SMARTCARD),  SCF_Terminal_get-
       Card(3SMARTCARD), attributes(5)

SunOS 5.10							    28 Feb 2001 					SCF_Card_reset(3SMARTCARD)
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