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I heard that too many paths could result in impact of storage infrastructure performance. Can somebody please answer why?

This is not regarding number of paths for a single server, but looking at whole infrastructure - what impact on FC switches/ storage array etc.

I remember at previous company I worked for we had a project to decrease number of paths as it had some performance hit on SAN / switches/ backend storage array (don'r remember details, but there we had Brocade switches and were migrating from EMC storage array to NetApp).

Quick googling didn't yield much results. Our DBA team has requested 20 voting disks for Oracle backend, 5Gb each and putting management overhead aside, I thought it could also have performance hit.

  • This is getting close voted because requests for learning materials are off-topic. However, it looks like you have a specific question and received an answer that addressed it. Can you edit the question to simply ask what you wanted to know instead of asking where you can find learning materials on the subject? – fixer1234 Jul 28 '18 at 20:25
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I'm afraid, I can't recommend you the article but I hope, you have already found a good source of information. If not, here what I can remember on the subject.

  • As I remember, a very rare problem with excessive number of ISLs could emerge in Brocade SAN when there are a really big number of switches and they are connected using full-mesh topology. I can be wrong, but it was related to FSPF when it's not able to enumerate all paths. I'm not sure if it's actual nowadays.

  • I think path number limiting may be welcome if the restrictive In-Order Delivery (IOD) policy is enabled on switches. But if IOD is enabled, it means you already faced issues with out-of-order frames (caused by ISL-flapping, etc) and devices that can't tolerate it, but you have to live as-is (for example, because you have long paths to a remote site).

  • Sequential operations are usually served faster by storage systems. So arrays try detecting sequential read-write operations to enable appropriate algorithms and provide better performance. Having excessive number of paths to the same LUN can sometimes confuse storage systems and they can start treating them like random IO without applying sequential optimisations.

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