acnsys
Enthusiast
Enthusiast

Max disk size for a LUN

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HI,

I have a 400GB LUN that i have mounted in VI Client as datastore (size 399,2GB). I want to dedicate that VMFS for a D drive on a VM, how big can i make it? If i give it the whole space, i guess it will not be good because there wont be anymore space for metadata.

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Lightbulb
Virtuoso
Virtuoso

I usually leave between 10-15% of Datastore uncommitted. If you intend to use snapshots you might want more free space.

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Lightbulb
Virtuoso
Virtuoso

I usually leave between 10-15% of Datastore uncommitted. If you intend to use snapshots you might want more free space.

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TomHowarth
Leadership
Leadership

Well the maximum size of VMDK you can create is directly related to the block size in your VMFS partition,

The Default size is 1MB with a block size of 1MB you will be able to create a VMDK of a maximum size of 256GB.

the other block sizes are

2MB = VMDK size 512GB

4MB = VMDK size 1024GB or 1TB

8MB = VMDK size 2048GB or 2TB

so the answer is if you are using the default block size 256GB, else you will be able to create a VMDK to the full size of the LUN.

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Tom Howarth

VMware Communities User Moderator

Blog: www.planetvm.net

Tom Howarth VCP / VCAP / vExpert
VMware Communities User Moderator
Blog: http://www.planetvm.net
Contributing author on VMware vSphere and Virtual Infrastructure Security: Securing ESX and the Virtual Environment
Contributing author on VCP VMware Certified Professional on VSphere 4 Study Guide: Exam VCP-410
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Lightbulb
Virtuoso
Virtuoso

Which addresses whether or not he/she can create a VMDK file to fill their whole datastore (I am guessing not). Still not a good idea to commit all available space on a datastore to vmdk files.

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icontender
Contributor
Contributor

Why not use RDM (raw disk mapping)? The benefits are: better performance and control from a SAN. If you have a Netapp, equallogic or other SAN infrastructure that supports LUN snapshots you can do lots of advance tasks in seconds. (LUN cloning, time based snapshots, LUN resize, share LUN with other hosts (clustering) )

TomHowarth
Leadership
Leadership

but you are still limited to 2TB

If you found this or any other answer useful please consider the use of the Helpful or correct buttons to award points

Tom Howarth

VMware Communities User Moderator

Blog: www.planetvm.net

Tom Howarth VCP / VCAP / vExpert
VMware Communities User Moderator
Blog: http://www.planetvm.net
Contributing author on VMware vSphere and Virtual Infrastructure Security: Securing ESX and the Virtual Environment
Contributing author on VCP VMware Certified Professional on VSphere 4 Study Guide: Exam VCP-410
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