HPE EVA Storage

EVA 4400, vSphere4 and path management

 
Mikkel Nielsen
Occasional Advisor

EVA 4400, vSphere4 and path management

Hi.

We have a EVA 4400, where i have set up 3 out of 6 LUN's to use "Path A-Failover/failback" and the other 3 to use "Path B-Failover/failback".

In vSphere all the LUN's are set to MRU, and as i understand the best practice whitepapers, this should work.

My problem is that all LUN's have "Controller 1" as the manageing controller and all paths is pointing to Controller 1.

Why can this be?
12 REPLIES 12
Uwe Zessin
Honored Contributor

Re: EVA 4400, vSphere4 and path management

because MRU is not ALUA-aware and uses the first active path it finds. After some time, the controller firmware recognizes for each virtual disk that the majority of I/Os goes through the same controller. In order to optimize the I/O processing it moves virtual disk ownership.
.
Mikkel Nielsen
Occasional Advisor

Re: EVA 4400, vSphere4 and path management

Im Sorry but thats not right.

Look at this i got from HP:

Title: HP Storageworks EVA - VMWare ESX 4.0/Vsphere Support for Roundrobin Path Selection Policy
Object Name: mmr_na-0259413
Document Type: Support Information--Informational
Original owner: Storage EVA
Disclosure level: Public
Version state: published
Information
Path selection and failback options included:
Fixed, Most Recently Used and Round Robin.

The Fixed path policy is recommended for A/A arrays. It allows the user to configure static load balancing of paths across ESX hosts. The MRU policy is recommended for A/P arrays. It prevents the possibility of path thrashing due to a partitioned SAN environment.

Round robin may be configured for either A/A or A/P arrays, but care must be taken to insure that A/P arrays are not configured to automatically switch controllers. If A/P arrays are configured to automatically switch controllers (sometimes called pseudo A/A), performance may be degraded due to path ping ponging.

Round Robin path selection policy is supported for EVA.
Details
In ESX4.0, ESX is ALUA compliant furthermore, Round Robin and MRU are ALUA aware. So they will both give priority to the Active-Optimized paths to the LUN. FIXED on the other hand in ESX 4.0 ignores all ALUA settings and sends I/O down to the selected path.

In the EVA configuration/user guide recommendates that the following LUN presentation policies are supported with VMware:
- No Preference
- Path A or B failover/failback

However if a Fixed path policy is used then re-use the same I/O paths as before failover and even if they are not optimal at first, the EVA will eventually make the path optimal. Using Fixed is much more tedious as fixed paths must be matched on all servers and all LUNs. So for simplicity, the LUN presentation should always be set to path A or B failover/failback alternating the LUN to path A and path B. MRU is now more suitable than Fixed because it is very likely that in a large ESX cluster more than one EVA port on the optimal controller for a LUN will be use for I/O by servers in the cluster without additional administrator intervention. But again, Round Robin really should be the setting of choice to maximize port utilization and significantly reduce configuration time.
Ole Thomsen_1
Trusted Contributor

Re: EVA 4400, vSphere4 and path management

I had the axact same experience with an EVA4100 until I changed path selection to RR. Upon that ESX instantly changed path to the dedicated controller.

BTW, this is the first vSphere/EVA path recommendation I have seen from HP, requested it several times with no luck.

Ole Thomsen
Mikkel Nielsen
Occasional Advisor

Re: EVA 4400, vSphere4 and path management

I have tried to change it to RR, but the selected path is still pointing to controller 1. :-(
Uwe Zessin
Honored Contributor

Re: EVA 4400, vSphere4 and path management

That can happen if the controller firmware has moved the ownership to Controller 1 despite any preferred path settings (it is only a hint...). Try to moved it back to Controller 2 with CV-EVA and then watch the VI-Client after 5 minutes or so.
.
Mikkel Nielsen
Occasional Advisor

Re: EVA 4400, vSphere4 and path management

That was i also thinking... :-)

But i cannot find anywhere in CV where i can change the ownership manually.
Uwe Zessin
Honored Contributor

Re: EVA 4400, vSphere4 and path management

- select the virtual disk's 'Properties' page

- press the [Presentation] tab

- select in:
-- Preferred path/mode: [Path ?-Failover/failback
- press [Save changes]

Maybe you need to use "No preference"+[Save changes] and then "Path ?-Failover/failback"+[Save changes] to force a change if your intended path was already set, but the ownership was moved.
.
Mikkel Nielsen
Occasional Advisor

Re: EVA 4400, vSphere4 and path management

This seems buggy.... :-)

After changing the the Preferred path/mode, to No Preference and the back to A and B, the LUN's using MRU also changes path....

So after a little testing, the result must be; when creating LUN's set them to No Perference, and then change it to A/B after it has been added to vmware.

Uwe Zessin
Honored Contributor

Re: EVA 4400, vSphere4 and path management

And what happens after a reboot of the ESX server? Does it still follow the ALUA hints when MRU is set? (not a rethorical question)
.