VMFS Extent

[dazzpowder]

Hello can anyone explain what adding an extent is compared to increasing the datastore size (grow volume on-line) .  If I expand the LUN that the datastore reside on and then add the space to the datastore is that different to adding an extent is the datastore effectively still 1 extent? what do people mean by adding an extent?

[a_p_ · Accepted solution]

In version prior to vSphere 4, the only way to increase the size of a datastore was to add another LUN (extent) to it, i.e. extending it. With vSphere 4.0, VMware added the option to grow a datastore, i.e. increase the VMFS partition size. The major difference is that increasing a datastore by adding another LUN, adds complexity and may even cause issues (think of a RAID 0, where one of the disks fails).

André

[bayupw]

See this post: VMFS Extents - Are they bad, or simply misunderstood? | VMware vSphere Blog - VMware Blogs

Below is some explanation that I copy from the blog post

What is an Extent?

A VMFS volume resides on one or more extents.

Each extent is backed by a partition on a physical device, such as a LUN.

Normally there will be only one extent for each LUN.

Extents are used when you create a VMFS volume, and more extents can added if you want to expand the volume.

VMware’s Best Practice/Recommendation for Extents

The only cases I can see where you might need extents are:

1. You are still on VMFS-3 and need a datastore larger than 2TB.

2. You have storage devices which cannot be grown at the back-end, but you need a datastore larger than 2TB.

There is nothing inherently wrong with extents, but the complexity involved in managing them has given them a bad name.

Below are some KBs & links related to VMFS growing & extents:

VMware KB: Growing or expanding a VMFS volume or datastore

VMware KB: Creating and managing extents on ESX/ESXi

VMFS Volume Extents Decision Factors -- Virtualization Review

Thanks,

Bayu

[vThinkBeyondVM]

Hi Friend,

Plz refer below resources.

VMFS Extents - Are they bad, or simply misunderstood? | VMware vSphere Blog - VMware Blogs

VMware KB: Growing or expanding a VMFS volume or datastore

[dazzpowder]

Thanks all, I have read many of the extent articles blogs and they never seem to be as clear as Andre's answers they all seem to talk about adding space by adding or growing an extent.  I have always expanded the LUN then increased the extent online.

[vThinkBeyondVM]

Yes I agree with you. Andre's answer is very clear.