Chapter 9 Managing Storage

4From the list of configured datastores, select the datastore whose paths you want to view or configure.

The Details panel shows the total number of paths being used to access the device and whether any of them are broken or disabled.

5Click Properties > Manage Paths to open the Manage Paths dialog box.

You can use the Manage Paths dialog box to enable or disable your paths, set multipathing policy, and specify the preferred path.

View Storage Device Paths

Use the vSphere Client to view which SATP and PSP the host uses for a specific storage device and the status of all available paths for this storage device.

Procedure

1 Log in to the vSphere Client and select a server from the inventory panel. 2 Click the Configuration tab and click Storage in the Hardware panel.

3Click Devices under View.

4Click Manage Paths to open the Manage Paths dialog box.

Setting a Path Selection Policy

For each storage device, the ESX host sets the path selection policy based on the claim rules defined in the /etc/vmware/esx.conf file.

By default, VMware supports the following path selection policies. If you have a third-party PSP installed on your host, its policy also appears on the list.

Fixed	The host always uses the preferred path to the disk when that path is available.
(VMW_PSP_FIXED)	If the host cannot access the disk through the preferred path, it tries the
	alternative paths. The default policy for active-active storage devices is Fixed.
Fixed AP	Extends the Fixed functionality to active-passive and ALUA mode arrays.
(VMW_PSP_FIXED_AP)
Most Recently Used	The host selects the path that it used recently. When the path becomes
(VMW_PSP_MRU)	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
	active-passive storage devices.
Round Robin	The host uses an automatic path selection algorithm rotating through all active
(VMW_PSP_RR)	paths when connecting to active-passive arrays, or through all available paths
	when connecting to active-active arrays. This implements load balancing across
	the physical paths available to your host.
	Load balancing is the process of spreading I/O requests across the paths. The
	goal is to optimize performance in terms of throughput, such as I/O per second,
	megabytes per second, or response times.

Table 9-1 summarizes how the behavior of host changes, depending on the type of array and the failover policy.

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ESX Configuration Guide

Table 9-1. Path Policy Effects

Policy/Controller	Active/Active	Active/Passive
Most Recently Used	Administrator action is required to fail back	Administrator action is required to fail back
	after path failure.	after path failure.

Fixed	VMkernel resumes using the preferred path
	when connectivity is restored.

VMkernel attempts to resume using the preferred path. This can cause path thrashing or failure when another SP now owns the LUN.

Round Robin	No fail back.	Next path in round robin scheduling is
		selected.
Fixed AP	For ALUA arrays, VMkernel picks the path set to be the preferred path.
	For both A/A and A/P and ALUA arrays, VMkernel resumes using the preferred path, but
	only if the path-thrashing avoidance algorithm allows the fail-back.

Change the Path Selection Policy

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.

Procedure

1 Open the Manage Paths dialog box either from the Datastores or Devices view.

2Select a path selection policy.

By default, VMware supports the following path selection policies. If you have a third-party PSP installed on your host, its policy also appears on the list.

n Fixed (VMW_PSP_FIXED)

n Fixed AP (VMW_PSP_FIXED_AP)

n Most Recently Used (VMW_PSP_MRU) n Round Robin (VMW_PSP_RR)

3For the fixed policy, specify the preferred path by right-clicking the path you want to assign as the preferred path, and selecting Preferred.

4Click OK to save your settings and exit the dialog box.

Disable Paths

You can temporarily disable paths for maintenance or other reasons. You can do so using the vSphere Client.

Procedure

1 Open the Manage Paths dialog box either from the Datastores or Devices view. 2 In the Paths panel, right-click the path to disable, and select Disable.

3Click OK to save your settings and exit the dialog box.

You can also disable a path from the adapter’s Paths view by right-clicking the path in the list and selecting

Disable.

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