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AIX 6227 Dual Fiber Channel

Posted on 2003-02-25
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Last Modified: 2013-12-16
Hello,

I've set-up the following

AIX 4.3.3 with 2 * 1Gb Fiber channel
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Cisco 4800 Fiber Switch
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SAN

Everything looks OK

Apart from the fact that I see the disks appearing twice. Has anyone else come across this, and any ideas how to resolve?
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Question by:mrn060900
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by:tfewster
ID: 8026890
This is normal if there is no LUN masking on the switch or SAN as the 2 x FC cards give you 2 routes to each LUN.  It's actually desirable in most situations - If your OS supports multi-pathing (e.g. with Veritas Volume Manager), it can automatically fail over from one channel to another in case of hardware failure. You may also be able to do load-balancing across the 2 FC cards.

If you really don't want this, you should only publish the LUN to one World Wide Name (i.e. only one of the FC cards).
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by:mrn060900
ID: 8032174
Thanks for the answer, but I was expecting multi-pathing, anyone know if AIX supports it?
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by:mrn060900
ID: 8032560
Thanks for the answer, but I was expecting multi-pathing, anyone know if AIX supports it?
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by:tfewster
ID: 8042099
After a conversation (in the pub) with a mate who works on  AIX: No, 4.3 does not support multi-pathing natively But it's not clear what happens if you try to configure in both LUNS.

If you have an IBM Shark array, you get the DPO (Dynamic Pathing Option?) software. Alternatively, Veritas Volume Manager software will do the job.

Multi-pathing is built in to AIX 5

If you've bought a SAN infrastructure, surely the supplier should be able to tell you what you can connect to it and what can be supported? It's in their interest to make you use more switch ports etc ;-)
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by:mrn060900
ID: 8042124
You would have thought they (SUN) could tell me what the supported config is. Anyway the answer is to install Hitachi Dynamic Link Manager, which allows you to set-up multipathing on AIX 4.3.3. God bless the pub & mates, thanks for your help
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by:tfewster
ID: 8045491
Get CS to PAQ this question (& refund your points so you could repost it in the new Storage TA ;-)

I've had similar problems with SAN suppliers, e.g. they will certify an HP A5158A FC card but won't even comment on another FC card with the same chipset, because they haven't tested every combination of hardware & operating system level...

Incidentally, you're lucky you only see 2 disks for every "real" disk; HP-UX & their supposedly-integrated version of the HDS disk array shows dozens of 0-size "placeholder" LUNS, making it very difficult to pick out the LUN you've just published to a host.  

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by:cjs2895
ID: 8265472
First, there is an bug in cfgmgr when dealing with multiple paths to FC attached devices (at least up until AIX 5.2 though I haven't tested it yet). You need to run cfgmgr on each channel seperately, or you may end up with missing or phantom devices. So something along the lines of:

  rmdev -Rdl fcsX # Do this for each channel
  cfgmgr -vl fcsX # Then do this for each channel

After you've done this you should have an hdisk device for every drive on every channel (4 drives * 2 channels = 8 hdisk devices). You will be able to look at the attributes with "lsattr -El hdiskX" to see the WWN of the drives.

To have multipathing for the drives you need to use whatever software came from your SAN vendor (EMC is PowerPath, Hitachi is DMP, Shark is VSS, etc.). They will create puesdo devices (ie hdiskpowerX on EMC) which combine the two hdisk devices under one virtual device that handles the multipathing functionality. You will use those virtual devices to create your volume groups and such on.

Without the multipathing software you will also run into locking conflicts (ie hdiskX on channel 1 will have PVID's and can be used, but its mirror on channel 2 will have no PVID and the system will respond its already in use). If you are a programmer and you are doing multipathing in your application (database perhaps?) you can break the locks with low-level ioctl()s.
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cjs2895 earned 1500 total points
ID: 8265480
To answer your secondary question, AIX 5.2 supports multipathing natively, though I'm not familiar with how its implemented, compatability with third party storage vendors, etc. Prior to AIX 4.3 you'll need your SAN vendor's software.
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