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November 8th, 2016 06:00
Two LUNs on one Storage Pool
Hello,
I've a question about two (or basicly multiple LUNs) on one Storage Pool. At first I created a SP with a total capacity of around 20 TB. Afterwards I created two equal sized LUNs. If I check the properties of the LUNs, they have a different "Distribution (%)" of the tiers. E.g. the Extreme Performance tier as 1,47% on LUN 1 and 5,73% on LUN 2.
My question: what happens, if all the "high performance I/O" happens on LUN 1 and LUN 2 has only NL-SAS related I/O? Will the distribution percentage of the Extreme Performance tier on LUN 1 increase and on LUN 2 decrease dynamicly?
Kind regards,
Dennis
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umichklewis
3 Apprentice
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1.2K Posts
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November 8th, 2016 14:00
This will change dynamically. FAST-VP uses metrics from the access history of data on the LUN to determine what to move between tiers. Unless you have 100% identical workloads on two LUNs all the time, you'll rarely see the same distribution values.
Let us know if that helps!
Karl
Rainer_EMC
4 Operator
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8.6K Posts
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November 8th, 2016 10:00
If you have FAST VP enabled then it will move parts of the LUN between tiers according to the I/O usage
see the VNX Fast VP White paper for more details
DennisHueckelhe
9 Posts
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November 8th, 2016 11:00
Yes, the FAST VP feature and the movement between the tiers is clear. My question was meant differently.
As you can see: LUN1 has 1,47% of Extreme Performance Tier and LUN2 has 5,73%. I don't understand how VNX allocate these distribution values, since both LUNs have the same size and using the same storage pool. I would expect that both LUNs have exactly the same half of all. Or can this distribution change dynamicly?
DennisHueckelhe
9 Posts
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November 9th, 2016 00:00
Yes, that helps me to understand how the VNX handle the distribution between multiple LUNs
I expected that it starts with a distribution of 50% for each and was confused that LUN2 gets much more than LUN1. But since the VNX adjust the distribution dynamicly, it should not matter which VM is stored on which LUN (the two LUNs are used as datastore for ESXi)
Rainer_EMC
4 Operator
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8.6K Posts
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November 9th, 2016 04:00
inital allocation adheres the to the FAST VP policy
either highest first or distribution according to tier capacities