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in blueprint - 09 Jan, 2016
by mordi - no comments
VCP6-DCV blueprint section 3:Configure and Administer Advanced vSphere 6.x Storage -Objective 3.3.

In this post we will continue covering the storage objective from the blueprint.To Better understand this objective I think we need to change the order and also some stuff in the list are redundant, so I will not follow subject by subject.

The following are the blueprint objective:

  • Explain common multi-pathing components
  • Differentiate APD and PDL states
  • Compare and contrast Active Optimized vs. Active non-Optimized port group states
  • Explain features of Pluggable Storage Architecture (PSA)
  • Understand the effects of a given claim rule on multipathing and failover
  • Explain the function of claim rule elements:
    • Vendor
    • Model
    • Device ID
    • SATP
    • PSP
  • Change the Path Selection Policy using the UI
  • Determine required claim rule elements to change the default PSP
  • Determine the effect of changing PSP on Multipathing and failover
  • Determine the effects of changing SATP on relevant device behavior
  • Configure/Manage Storage Load Balancing
  • Differentiate available Storage Load Balancing options
  • Differentiate available Storage Multi-pathing Policies
  • Locate failover events in the UI

 


PSA – Pluggable Storage Architecture :

PSA1

Source: VMware vSphere Storage document

 

Within VMkernel we have the following components:

  • PSA -Which stand for Pluggable Storage Architecture
  • NMP -Native Multipathing Plug-In , which is the VMware multipathing module
  • MPP -Third-Party multipathing module

The VMware NMP includes:

  • PSP -Path Selection Plug-In, which handles paths for for a given device
  • SATP-Storage Array Type Plug-In, which handles path failover for a given storage array.

 

Lets start with PSP:

as mention PSP handle the path selection which we have three policies for that:

  • MRU – Most recently used , When the path becomes unavailable, the host selects an alternative path. The host does not revert back to the original path when that path becomes available again. Default for ACTIVE-PASSIVE storage device.
  • Fixed – The host uses the designated preferred path, if it has been configured.Otherwise, it selects the first working path discovered at system boot time.Default for ACTIVE-ACTIVE  storage device.
  • Round Robin (RR) – The host uses an automatic path selection algorithm rotating through all active paths
    available paths when connecting to active-active arrays. RR is the only load balancing policy. 

To assign a policy via the GUI: Under Storage >> Select datastore>>Setting >>Connectivity and multipathing >> host >> edit multipathing

PSA2

To see it via the CLI , run the following command:  esxcli storage nmp psp list

PSA3

SATP:

As mention before SATP is Storage Array Type Plug-In, which handles path failover for a given storage array.We can see the SATP policies only via the CLI (Get used to it).To see it via the CLI , run the following command:  esxcli storage nmp satp list

PSA4

 


Claim rules:

When you start your ESXi host or rescan your storage adapter, the host discovers all physical paths to storage devices available to the host. Based on a set of claim rules, the host determines which multipathing plug-in (MPP) should claim the paths to a particular device and become responsible for managing the multipathing support for the device.

 

Before we change the policy lets see what devices are connected,run the following command:  esxcli storage nmp device list .Here we can see that the SATP and PSP for out lab iSCSI device.

PSA5

To see the rule list ,run the following command: esxcli storage core claimrule list. 

PSA6

Here you can see the rules for new devices.the rules are in order(think about it like a firewall if it meet it it not going down the list), you can see that usb/sata/ide all get the default plugin which is NMP, and at the end of the list , it will assign NMP plugin for anything else.(This can be changed)

 

Determine required claim rule elements to change the default PSP:

Basically you need to define new default policy: AS you can see in the pic below the default PSP for VMW_SATP_DEFAULT_AA is Fixed , to change it to MRU we ran the command :  esxcli storage nmp satp set -s VMW_SATP_DEFAULT_AA -P VMW_PSP_MRU . We listed it again to confirm the change.

PSA7

 

Compare and contrast Active Optimized vs. Active non-Optimized port group states:

I think VMware refers to ALUA (Asymmetric Logical Unit Access) connection.

When we have two paths to the storage and one is “Fast”(optimized) and the other one is “Slow”(non optimized)

  • The defaults PSP for all VMW_SATP_ALUA is MRU
  • The MRU select the optimized path from the VMW_SATP_ALUA or un-optimized path id there is no optimized path.
  • will use the above path until better path available

 


Differentiate APD and PDL states:

APD: All Paths Down , happens when storage device loose all paths to the host.

  • The operational state of the device changes to Dead or Error.
  • All paths are shown as Dead.
  • Datastores on the device are dimmed.

PDL:Permanent Device Loss, happen when storage device permanently fails or is administratively removed or excluded.

  • The operational state of the device changes to Lost Communication.
  • All paths are shown as Dead.
  • Datastores on the device are grayed out.

 


Locate failover events in the UI:

You will need to “Decode” the /var/log/vmkernel.log . Please refer to this VMware KB 1003433 document : http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1003433 . to get more clues about the failover event.

 

Thanks for reading

Mordi.

 

 

 

 

 

 

 


 

 

 

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