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1 Rookie
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4 Posts
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1125
September 29th, 2013 23:00
Pros and cons of using both ports for single processor on VMAX FA
VMAX FA port 0 and 1 of any FA director share the same processor like FA-1E0 and FA-1E1 use same processor. That mean IOPS supported with FA-1E would shared.
My question is if we use only ports 0 of all FA and leaving port 1 unused then what are Pros and cons of this ? Assuming we don't cross the mapping limit of FA i.e. we have less devices than can be mapped to any FA.
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PedalHarder
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465 Posts
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September 30th, 2013 02:00
Correct, no additional IOPS out of using both ports on the same processor. If you have large IO size and want large throughput, you will get more throughput from both ports combined than a single port. Not double though since you will still likely run out of IOPS capability before hitting bandwidth limit.
Since an FA will typically run out of IOPS before bandwidth, you are saving a switch port by not using the second port on the processor. i.e. One port is usually plenty to fully exercise the FA CPU.
sauravrohilla
859 Posts
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September 30th, 2013 05:00
In addition to Jason response, if you map your LUN to same port of the processor and if its the windows cluster then your cluster validation might fail.
regards,
Saurabh
sauravrohilla
859 Posts
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September 30th, 2013 06:00
ETA emc220390: Symmetrix 8000, DMX, and VMAX: Cluster environments that require setting the PER bit and have a single HBA configured to both the A and B port of an FA have not been qualified and could experience validation or failover issues
https://emc--c.na5.visual.force.com/apex/KB_ETA?id=kA37000000000KK
Symmetrix: Windows 2008 Cluster validation and disk arbitration are failing for hosts attached to both A and B ports of same FA (ex: 7Aa and 7Ab)
https://emc--c.na5.visual.force.com/apex/KB_BreakFix_1?id=kA1700000000IfG
thom_chandresh
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September 30th, 2013 06:00
Can you elaborate more on cluster validation issue ?
Chandresh
Quincy561
1.3K Posts
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September 30th, 2013 08:00
You should NEVER assign the same device to both ports of the same FA CPU. As stated before, there won't be any performance benefit, and no added availability should something happen to the director.
You can share the two ports on one CPU with different hosts and LUNs however. IO tends to arrive in bursts, and it is not likely the bursts from different LUNs and hosts will arrive at exactly the same time. Also if you have workloads that are not active at the same time (such as transactional and backup) those would be perfect cases for sharing the 0 and 1 ports.
AranH1
2.2K Posts
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September 30th, 2013 08:00
Being that they share the same FA processor the device count limit applies to the FA, not the ports, so you won't be able to map more devices using both ports. And as Jason pointed out you won't necessarily see more performance using both ports. And definitely DO NOT map a device down both ports to a host.
All of that considered the only value I really see in deployments for using both ports of an FA is for enforcing host isolation due to FA port settings requirements. With the ability to enable/disable the majority of settings using the initiator group flags, this is less and less common.
IMO the second port isn't very useful since they both share the same processor, and I usually see VMAX arrays deployed with the second port just not cabled up.