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IO on Logical Disk

 
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kisalipa
Occasional Advisor

IO on Logical Disk

Hi Friends,

Suppose I created a Vvol on a Inserv V450, the LD's will be equally created on all 4 nodes. And I exported the vvol to a Host. Now I have zoned the Host to 2 nodes (Node 0 and 2) only. Now when the Host writes the data, the data will be written on LD's of Node 0 and 2. How the data will be passed on the LD's on Node 1 and 3?

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Sheldon Smith
Honored Contributor

Re: IO on Logical Disk

No no no. :) You zoned the Host to 2 nodes (Node 0 and 2) only. When the Host writes the data, the data will be received on ports of Node 0 and 2. The receiving controller looks at the IO request and passes it along to it ASIC(s). The ASICs are in a full-mesh connection and pass data between each other (and between LDs).
Take a look at the HPE 3PAR StoreServ Architecture whitepaper - 4AA3-3516ENW

While you are at it, take a look at the HPE 3PAR StoreServ Storage best practices guide - 4AA4-4524ENW
"Best practice: Hosts should be mirrored to node pairs. For example: zoned to nodes 0 and 1 or nodes 2 and 3. Hosts should not be zoned to non-mirrored nodes, such as 0 and 3."

These and other white papers as well as all 3PAR documentation are available at the Hewlett Packard Enterprise Information Library. Or use your favorite search engine and look for the document's ID number (above).


Note: While I work for Hewlett Packard Enterprise, all of my comments (whether noted or not), are my own and are not any official representation of the company.
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kisalipa
Occasional Advisor

Re: IO on Logical Disk

Thanks for the explanation Sheldon. Just to confirm, in the same example, when an IO (write) is received on Node 0 and 1, will the data be written on all LD's present in all Nodes (0,1,2 and 3) through ASIC mesh connectivity??

 

Sheldon Smith
Honored Contributor
Solution

Re: IO on Logical Disk

Yes, that's what the full-mesh provides. An IO request coming in on any node may be passed to any other node's LDs in the system.


Note: While I work for Hewlett Packard Enterprise, all of my comments (whether noted or not), are my own and are not any official representation of the company.
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Dennis Handly
Acclaimed Contributor

Re: I/O on Logical Disk

> when a write is received on Node 0 and 1, will the data be written on all LDs present in all Nodes

 

To be clear, a given LD is always matched to a given offset in the VV.  (With differences for dedup and compression.)

kisalipa
Occasional Advisor

Re: I/O on Logical Disk

Hi Dennis,

Sorry could not understand what you meant by - 'a given LD is always matched to a given offset in the VV'?? Could you please elaborate?

Dennis Handly
Acclaimed Contributor

Re: I/O on Logical Disk

If you write to a giving block offset in a VLUN, you are writing to the same LD each time.

It doesn't matter that node/port gets the I/O request.

showblock can be used to determine the mapping of offsets in VV, LD and PDs.