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esx san paths

Posted on 2010-11-22
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Last Modified: 2012-05-10
hi
i have two esx servers connected via fibre cable to a san. i have two hbas in each esx , one cabelled to each san controller etc. when i go into the properties of a lun, i see two paths, one is active and has a green diamond beside it and the other just says on. does this mean that one is the live path and the other comes to life is the active one goes down? do they not load balance?
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Question by:mikeleahy
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David earned 125 total points
ID: 34189493
No, they do not.  Load balancing software is an add-on that is typically offered by your storage vendor.  Sure some HBAs have some path failure software, which are somewhat generic, but load balancing is a whole 'nuther can of worms.  Contact your SAN hardware vendor for advice and pricing.
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by:mikeleahy
ID: 34189535
thanks, thats fine. so theoretically if one of the hbas was re-directed to a different san for example, there would be no slowdown in response from the other hba as only one was being used anyway?
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by:vnekic
vnekic earned 125 total points
ID: 34189652
well.. let me start by saying you have to know the SAN.  They are different at times.  But, in most cases... they are not very smart.

This means that you CAN have 2 paths active and pointing to the same LUN.  Which is what you want.

Then from the ESX server you control the management.
First.. you will have BOTH your paths set up in Configuration > Storage Adapters of the ESX machine.

Then from configuration > Storage > (SAN) > Properties > MANAGE PATHS

You will control the path selection.

There you will see the GREEN diamond etc.. of what is live

Why most for HA systems will have 2 SAN Switches to the SAN.  Now, if one fails, the other can take over.

Take a look there and of course talk to your hardware vendor as mentioned by our Genius ;)

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by:mikeleahy
ID: 34189880
thanks
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Expert Comment

by:David
ID: 34190152
Also since you have 2 different servers connected to the same device (I assume), then if they are both active, they will gladly walk all over each other and destroy your data whenever one host writes data that was cached.

I.e,  the selected offset currently holds "ABC"

BOth read, both have ABC in cache.

One host changes to "DEF", and writes, and it is still in cache.

Now at this point,  one server says data contains ABC, the other says it contains DEF, because the CACHED data is different.
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