How to Create a Virtual SSD for vSphere 5.5 vFlash

Using a virtual solid-state drive can be a handy way to save time and money for certain vSphere tasks.

One of my favorite upgrades in VMware's vSphere 5.5 is Flash Read Cache, or vFlash. It's integrated with vCenter 5.5, high availability (HA), distributed resource scheduler (DRS) and vMotion.

vFlash uses a portion of a local physical Solid State Drive (SSD) drive in a vSphere infrastructure to allow for a high-performance read cache layer for the ESXi Host.  The other very nice benefit is that vFlash offloads I/O from your SAN to the vFLash local, physical SSD. As a result, the ESXi host provides lower application latency to its hosted virtual machines (VMs) and their applications.

I needed to speed up the performance of the applications running on some of my VMs under a proof of concept environment, so I decided to use vFlash. However, I didn't have a physical SSD, so I created a virtual SSD. I did it by tricking vSphere into accepting a virtual SSD in lieu of a physical one.

The process of creating a virtual SSD is straightforward. While it's not a permanent substitute for a physical SSD, it works for testing in an ESXi lab environment. Virtual SSDs save money on hardware, without causing a big impact on performance. Here are the steps for creating the virtual SSD:

Create a physical local virtual disk on the ESXi Host(s) that you want to enable vFlash. Ensure that the local virtual SSD size doesn't exceed the size of the physical ESXi host's local virtual disk.

Locate the ESXi host's local virtual disk path (e.g., mpx.vmhba1:C0:T0:L0).

Open a Secure Shell (SSH) session to each ESXi host you'll be configuring with a local virtual SSD.

Convert the physical local virtual disk to a local virtual SSD. Utilize the following esxcli command strings for the conversion.

The Storage Array Type Plugin (SATP) will allow your storage I/O to be load balanced properly by vCenter while using this new virtual disk. Here's the code that creates an SATP rule and enables the SSD string:

~ # esxcli storage nmp satp rule add -s VMW_SATP_LOCAL -d  mpx.vmhba1:C0:T0:L0 -o enable_ssd

Next, verify the SATP rule creation:

~ # esxcli storage nmp satp rule list | grep enable_ssd

Output:

VMW_SATP_LOCAL         mpx.vmhba1:C0:T0:L0                                           

enable_ssd             user

Next comes reclamation of the new virtual SSD, to enable application of the SATP rule:

~ # esxcli storage core claiming reclaim -d mpx.vmhba1:C0:T0:L0

Finally, confirm that the new virtual SSD has been created:

~ # esxcli storage core device list -d mpx.vmhba1:C0:T0:L0

Output:

mpx.vmhba1:C0:T2:L0

  Display Name: Original VM  Disk (mpx.vmhba1:C0:T0:L0)

  Has Settable Display Name:  false

  Size: 5120

  Device Type: Direct-Access

  Multipath Plugin: NMP

  Devfs Path: /vmfs/devices/disks/mpx.vmhba1:C0:T0:L0

  Vendor: VMware

  Model: Virtual disk

  Revision: 1.0

  SCSI Level: 2

  Is Pseudo: false

  Status: on

  Is RDM Capable: false

  Is Local: true

  Is Removable: false

  Is SSD: true

  Is Offline: false

  Is Perennially Reserved:  false

  Thin Provisioning Status:  unknown

  Attached Filters:

  VAAI Status: unsupported

Other UIDs:  vml.0000000000577d274761343a323a47

Once you verify that the Is SSD entry is true, the local disk is now a virtual one. You can use the GUI or the following command to refresh vSphere's storage:

~ #vim-cmd hostsvc/storage/refresh

Now that your virtual SSD is created and verified, you can add it to your ESXi host(s) and start using the vFlash feature. vFlash is easy to set up – just configure it in the vCenter Web client.

Setting Up vFlash:

1. In the vSphere Web Client, navigate to the host.

2. Click the Manage tab and click Settings.

3. Under Virtual Flash, select Virtual Flash Resource Management, then click Add Capacity.

4. From the list of available SSD devices, select the newly-created local virtual SSD drive to use for virtual flash and click OK.

A Few Warnings

Now that you have vFlash configured and operational, you can now start enjoying its benefits. Remember to ensure that you have VM version 10, or your VMs ill not benefit from the vFlash benefits. I also recommend that you have the vFlash configured for each ESXi Host.  I learned this lesson through initial trial and error while  conducting a vMotion session.  The VM will fail during a vMotion session if each ESXi Host doesn't have vFlash configured.

At this point, your vFlash will start providing the increased storage read and write speeds and reduced storage I/O contention. The best part is that you're utilizing a virtual SSD in lieu of a physical SSD, while maintaining the vFlash benefits, saving on hardware and operating your lab environment within a budget.