VCAP5-DCA Objective 1.3 – Configure and manage complex multipathing and PSA plugins

Objectives

  • Install and Configure PSA plug-ins
  • Understand different multipathing policy functionalities
  • Perform command line configuration of multipathing options
  • Change a multipath policy
  • Configure Software iSCSI port binding

Install and Configure PSA plug-ins

Official Documentation:
vSphere Storage Guide
, Chapter 17, “Understanding Multipathing and Failover , page 153.

Summary:
Starting from page 158, the vSphere Storage guide presents a very clear explanation on the pluggable Storage Architecture. Some highlights.

Figure 1 – Graphic provided by VMware

PSA: Pluggable Storage Architecture, makes multi pathing flexible and allows for 3rdparty multi pathing plug-ins(MPP). PSA is a special layer in the VMkernel.

MPP: Multi Pathing Plug-ins, discover physical storage devices and determine “claim rules” to export a logical device. MPP can coexist with NMP and can be used on a LUN or per array basis.

NMP: Native Multi Pathing Plugin, is from VMware. NMP manages sub plug-ins with SATP (storage array-type plug-ins) and PSP (path selection plug-ins) being the defaults

SATP: Storage Array-Type Plug-ins, do Path failover

PSP: Path Selection Plug-in, do Path load balancing

Installation of 3rdparty PSA plug-ins depends on the supplier. For Example, Dell Equallogic provides detailed instructions how to install their “Multipathing Extension Module”, a PSP module. Options for installing are:

  • Using vCenter Update Manager
  • Using Dell’s custom setup.pl script
  • Using vSphere CLI for ESXi

After finishing the installation, all available Datastores have their PSP automatically changed to the newly installed module.

Other references:

  • See also Objective 1.1, section Understand and apply LUN masking using PSA‐related commands

Understand different multipathing policy functionalities

Official Documentation:
vSphere Storage Guide, Chapter 17, “Understanding Multipathing and Failover , page 163, presents an overview of the default path selection policys.

Summary:
Three PSPs are available by default:

  • MRU (most recently used)
    The host selects the path that it used most recently. 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. There is no preferred path setting with the MRU policy. MRU is the default policy for most active-passive storage devices.
  • 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. If you want the host to use a particular preferred path, specify it manually. Fixed is the default policy for most active-active storage devices.
  • Round Robin
    The host uses an automatic path selection algorithm rotating through all active paths when connecting to active-passive arrays, or through all available paths when connecting to active-active arrays. RR is the default for a number of arrays and can be used with both active-active and active-passive arrays to implement load balancing across paths for different LUNs

Other references:

  • A

Perform command line configuration of multipathing options

Official Documentation:
vSphere Storage Guide, Chapter 17, “Understanding Multipathing and Failover , page 164, presents an overview of the available commands.

Summary:
The one and only command to manage PSA multipathing plug-ins is the esxcli command.

The section Managing Storage Paths and Multipathing Plug-Ins starts with a few important considerations. To highlight a few:

  • If no SATP is assigned to the device by the claim rules, the default SATP for iSCSI or FC devices is VMW_SATP_DEFAULT_AA. The default PSP is VMW_PSP_FIXED.
  • By default, the PSA claim rule 101 masks Dell array pseudo devices. Do not delete this rule, unless you want to unmask these devices

List Multipathing Claim Rules for a ESXI host:

~ # esxcli storage core claimrule list -c=MP

Rule Class   Rule  Class    Type       Plugin     Matches
----------  -----  -------  ---------  ---------  ---------------------------------
MP              0  runtime  transport  NMP        transport=usb
MP              1  runtime  transport  NMP        transport=sata
MP              2  runtime  transport  NMP        transport=ide
MP              3  runtime  transport  NMP        transport=block
MP              4  runtime  transport  NMP        transport=unknown
MP            101  runtime  vendor     MASK_PATH  vendor=DELL model=Universal Xport
MP            101  file     vendor     MASK_PATH  vendor=DELL model=Universal Xport
MP          65535  runtime  vendor     NMP        vendor=* model=*

This example indicates the following:

  • The NMP claims all paths connected to storage devices that use the USB, SATA, IDE, and Block SCSI transportation.
  • You can use the MASK_PATH module to hide unused devices from your host. By default, the PSA claimrule 101 masks Dell array pseudo devices with a vendor string of DELL and a model string of Universal Xport.
  • Any paths not described in the previous rules are claimed by NMP.

The Rule Class column in the output describes the category of a claim rule. It can be:

  • MP (multipathingplug-in),
  • Filter, or
  • VAAI.

The Class column shows which rules are defined and which are loaded.

  • The file parameter in the Class column indicates that the rule is defined.
  • The runtime parameter indicates that the rule has been loaded into your system.

For a user-defined claim rule to be active, two lines with the same rule number should exist, one line for the rule with the file parameter and another line with runtime. Several low numbered rules, have only one line with the Class of runtime. These are system-defined claim rules that you cannot modify.

Display Multipathing Modules

~ # esxcli storage core plugin list

Plugin name  Plugin class
-----------  ------------
NMP          MP

Display SATPs for the Host

~ # esxcli storage nmp satp list

Name                 Default PSP       Description
-------------------  ----------------  ------------------------------------------
VMW_SATP_MSA         VMW_PSP_MRU       Placeholder (plugin not loaded)
VMW_SATP_ALUA        VMW_PSP_MRU       Placeholder (plugin not loaded)
VMW_SATP_DEFAULT_AP  VMW_PSP_MRU       Placeholder (plugin not loaded)
VMW_SATP_SVC         VMW_PSP_FIXED     Placeholder (plugin not loaded)
VMW_SATP_EQL         VMW_PSP_FIXED     Placeholder (plugin not loaded)
VMW_SATP_INV         VMW_PSP_FIXED     Placeholder (plugin not loaded)
VMW_SATP_EVA         VMW_PSP_FIXED     Placeholder (plugin not loaded)
VMW_SATP_ALUA_CX     VMW_PSP_FIXED_AP  Placeholder (plugin not loaded)
VMW_SATP_SYMM        VMW_PSP_FIXED     Placeholder (plugin not loaded)
VMW_SATP_CX          VMW_PSP_MRU       Placeholder (plugin not loaded)
VMW_SATP_LSI         VMW_PSP_MRU       Placeholder (plugin not loaded)
VMW_SATP_DEFAULT_AA  VMW_PSP_FIXED     Supports non-specific active/active arrays
VMW_SATP_LOCAL       VMW_PSP_FIXED     Supports direct attached devices
~ #

Display NMP Storage Devices

~ # esxcli storage nmp device list

naa.5000144f80206240
Device Display Name: EMC iSCSI Disk (naa.5000144f80206240)
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type Device Config: SATP VMW_SATP_DEFAULT_AA does not support device configuration.
Path Selection Policy: VMW_PSP_FIXED
Path Selection Policy Device Config: {preferred=vmhba35:C0:T1:L0;current=vmhba35:C0:T1:L0}
Path Selection Policy Device Custom Config:
Working Paths: vmhba35:C0:T1:L0

naa.5000144f77827768
Device Display Name: EMC iSCSI Disk (naa.5000144f77827768)
Storage Array Type: VMW_SATP_DEFAULT_AA
Storage Array Type Device Config: SATP VMW_SATP_DEFAULT_AA does not support device configuration.
Path Selection Policy: VMW_PSP_FIXED
Path Selection Policy Device Config: {preferred=vmhba35:C0:T0:L0;current=vmhba35:C0:T0:L0}
Path Selection Policy Device Custom Config:
Working Paths: vmhba35:C0:T0:L0

For other commands like masking paths, see section 1.1” Understand and apply LUN masking using PSA‐related commands”

Other references:

  • A

Change a multipath policy

Official Documentation:
vSphere Storage Guide, Chapter 17, “Understanding Multipathing and Failover , page 163, describes how to change the Path selection Policy

Summary:
VMware states:  “Generally, you do not have to change the default multipathing settings your host uses for a specific storage device. However, if you want to make any changes, you can use the Manage Paths dialog box to modify a path selection policy and specify the preferred path for the Fixed policy”

Multipath settings apply on a per Storage basis. Use the vSphere Client and from the “Hosts and Clusters” View, go to Configuration, Hardware, Storage and Select the Datastore of your choice. Open the Manage Paths dialog and select the desired policy.

Figure 2

Other references:

  • A

Configure Software iSCSI port binding

Official Documentation:
vSphere Storage Guide, Chapter 9, “Configuring iSCSI Adapters and Storage”, section “Configuring Software iSCSI Adapter” page 74, describes the complete process.

Summary:
Until vSphere 5, configuring the Software iSCSI adapter was a little bit complicated process, especially when you also wanted to configure Jumbo frames (Who does not want that?). You were not able to do the job using the vSphere Client, some portions needed to be done from the CLI. But from now on the whole process can be performed using the vSphere Client.

Chapter 9 in the vSphere Storage Guide nicely describes the whole process. I have also noticed that Storage vendors often publish manuals which describes the whole process on configuring a specific storage device in conjunction with vSphere.

The complete workflow includes:

  1. Activate the software iSCSI adapter.
  2. Configure networking for iSCSI.
    Configuring the network involves creating a VMkernel interface for each physical network adapter that you use for iSCSI and associating all interfaces with the software iSCSI adapter.
  3. If needed, enable Jumbo Frames.
  4. Configure discovery information.
  5. (Optional) Configure CHAP parameters.

Figure 3

Other references:

  • Nice video from Eric Sloof, configuring the iSCSI Software Adapter
  • Example, configuring iSCSI with VMware vSphere 5 and Dell Equallogic PS Series Storage
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One Response to VCAP5-DCA Objective 1.3 – Configure and manage complex multipathing and PSA plugins

  1. […] Summary: Multipathing, PSA and the related commands have been discussed in Objective 1.3 “Configure and manage complex multipathing and PSA plugins”. […]

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