VMFS Datastores
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Using a VMFS Datastore with ESX/ESXi
Use VMFS datastores whenever possible:
- VMFS is optimized for storing and accessing large files.
- A VMFS can have a maximum volume size of 64TB.
- NFS datastores are great for storing virtual machines. But some functions are not supported.
- Use RDMs if your virtual machine:
- Is performing SAN snapshotting
- Is clustered to a physical machine using Microsoft Cluster Service (MSCS)
- Has large amounts of data that you do not want to convert into a virtual disk
Creating a VMFS Datastore
To create a VMFS datastore:
- Select your host in the inventory and click the Configuration tab.
- Select Storage from the Hardware list. Click the Add Storage link.
- Complete the Add Storage wizard:
- Select Disk/LUN as the storage type.
- Select a device to use for your datastore. The Current Disk Layout page appears. If the disk you are formatting is blank, the Current Disk Layout page presents the entire disk space to you for storage configuration. If disk is not blank, you can choose to use the entire device or use only the free space on the device.
- Enter a datastore name. Choose a descriptive name, one that reflects the purpose or function of the datastore or of the hardware characteristics of the device itself.
- Specify the maximum size of the VMFS datastore.
- After the VMFS datastore is created, view its properties by selecting the VMFS datastore in the Storage list on the host’s Configuration tab.
Viewing VMFS Datastores
Clicking the Storage link in your host’s Configuration tab is one way to view information about your VMFS datastores. Another way is to view the Show all Datastores report in your host’s Storage Views tab.
Browsing Datastore Contents
The Datastores pane of the Configuration tab lists all datastores currently configured for the ESX/ESXi host.
To display the Datastores pane:
- Select your host in the inventory.
- Click the Configuration tab.
- Click the Storage link.
From the Datastores pane you can also browse the contents of a datastore. To do this, right-click the datastore and select Browse Datastore.
Managing Overcommitted Datastores
An overcommitted datastore occurs when there are many thin-provisional virtual disks that use close to their maximum allotted disk space.
Actively monitor your datastore capacity:
- Alarms assist through notifications:
- Datastore disk overallocation
- Virtual machine disk usage
- Use reporting to view space usage
Actively manage your datastore capacity:
- Increase datastore capacity when necessary.
- Use VMware Storage vMotion to mitigate space usage issues on a particular datastore.
Increasing the Size of a VMFS Datastore
When you need to create virtual machines on a datastore, or when the virtual machines running on this datastore require more space, you can dynamically increase the capacity of a VMFS datastore if the datastore has insufficient disk space.
Use one of the following methods:
- Add an extent to the VMFS datastore – An extent is a partition on a LUN. You can add a new extent to any VMFS datastore. The datastore can stretch over multiple extents, up to 32.
- Expand the VMFS datastore – Increase the size of the VMFS datastore within its extent. Only extents with free space immediately after them are expandable. As a result, rather than adding the new extent, you can expand the existing extent so that it fills the available adjacent capacity.
Comparing Methods for Increasing VMFS Datastore Size
The method that you choose to expand your VMFS datastore with depends on what you want to do.
For example, one reason for adding an extent to the datastore, instead of expanding the datastore within the extent, is to create a VMFS datastore greater than 2TB in size. The maximum size of a VMFS extent is 2TB. If your VMFS datastore consists of one extent, extents must be added if you want to increase the size of your VMFS datastore past 2TB. For example, a 6TB VMFS datastore is made of three extents.
An example of expanding the datastore within the extent instead of adding an extent to the datastore: Your storage admin has given you a 50GB LUN on which you format a VMFS datastore. Over time, your VMFS datastore fills up and you ask your storage admin to expand the LUN to 100GB. After the underlying LUN is increased (using array management utilities), you dynamically expand the datastore within the extent to use the newly available space. By starting out with a smaller LUN and expanding as needed, you can prevent wasting disk space and money.
Before increasing the Size of a VMFS Datastore
Generally, before making any changes to your storage allocation:
- Perform a rescan to ensure that your host sees the most current storage.
- Quiesce I/O on all disks involved.
- Note the unique identifier (for example, the NAA ID) of the volume that you want to expand.
Deleting a VMFS Datastore
You can delete any type of VMFS datastores, including copies of VMFS datastores that you have mounted without resignaturing. Deleting a datastore destroys the pointers to the files on the datastore, so the files disappear from all hosts that have access to the datastore. Deleting a VMFS datastore permanently deletes the pointers to the files on the datastore, so the files cannot be retrieved.
To delete a VMFS datastore:
- Click the Storage link in the host’s Configuration tab.
- Right-click the VMFS datastore and select Delete. When prompted, confirm the datastore removal.
Multipathing with Fibre Channel
To maintain a constant connection between a host and its storage, ESX/ESXi supports multipathing. Multipathing is a technique that lets your use more than one physical path for transferring data between the host and an external storage device.
In a failure of an element in the SAN network, such as HBA, switch, or cable, ESX/ESXi can fail over to another physical path. In addition to path failover, multipathing offers load balancing. Load balancing id responsible for redistributing I/O loads between multiple paths, thus reducing or removing potential bottlenecks.
To supports multiple paths with Fibre Channel SAN, the ESX/ESXi host typically has two or more HBAs available, from which the storage array can be reached through one or more switches. Or the setup might include one HBA and two SPs so that the HBA can use a different path to reach the disk array.
Multipathing with iSCSI Storage
When setting up your ESX/ESXi host for multipathing and failover, you can use multiple hardware iSCSI adapters or multiple NICs, depending on the type of iSCSI initiators on your host.
With hardware iSCSI, the host typically has two or more hardware iSCSI adapters available, from which the storage system can be reached using one or more switches. Alternatively, the setup might include one adapter and two storage processors so that the adapter can use a different path to reach the storage system.
With software iSCSI and dependent hardware iSCSI, you can use multiple NICs that provide failover for iSCSI connections between your host and iSCSI storage systems.
For this setup, because multipathing plug-ins do not have direct access to physical NICs on your host, you first need to connect each physical NIC to a separate VMkernel port. You then use a port-binding technique to associate all VMkernel ports with the iSCSI initiator. As a result, each VMkernel port connected to a separate NIC becomes a different path that the iSCSI storage stack and its multipathing plug-in can use.
Managing Multiple Storage Paths
Multiple paths can exist to a datastore on an ESX/ESXi host.
To configure multiple paths:
- Click the host’s Configuration tab.
- Click the Storage link.
- Right-click the datastore and select Properties.
Configuring Storage Load Balancing
The following path selection policies are supported for multipathing with FIbre Channel or iSCSI:
- Fixed – The host always uses the preferred path to the disk when that path is available. If it cannot access the disk through the preferred path, it trues the alternative paths. Fixed is the default policy for active-active storage devices.
- Most Recently Used - The host uses the most recent path to the disk until this path becomes unavailable. That is, the host does not revert back to the preferred path. Most Recently Used is the default policy for active-passive storage devices and is required for those devices.
- Round Robin – The host uses a path-selection algorithm that rotates through all available paths. In addition to path failover, the Round Robin policy supports load balancing across the paths. Before using this policy, check with storage vendors to find out if a Round Robin configuration is supported on their storage.
To set the path selection policy:
- In the datastore Properties dialog box, click Manage Paths.
- Select the path selection policy from the Path Selection drop-down menu.
Pluggable Storage Architecture
The Pluggable Storage Architecture (PSA) is a VMkernel layer responsible for managing multiple storage paths. PSA is a collection of VMkernel APIs that allow third-party vendors to insert code directly into the ESX/ESXi storage I/O path. This code is called multipathing plug-ins (MPPs). PSA allows third-party vendors to add support for new arrays into ESX/ESXI without having to provide internal information or intellectual property about the array to VMware.
VMware, by default, provides generic MPP called Native Multipathing Plug-in (NMP). PSA coordinates the operation of the NMP and third-party MPPs.
VMware uses PSA for its native load-balancing and failover mechanisms. Examples of VMware path selection policies (PSPs) included Round Robin (RR), Most Recently Used (MRU), and Fixed.
