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The purpose of Vmware Thin Disk

Posted on 2016-10-23
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Last Modified: 2016-10-23
If I understand when you create VM with Thin disk you allocate a disk size , for instance 40GB.
I have read that the actual size of the disk is based on the size of the Data written to disk on demand up to the size of 40GB that has been allocated.

If the VM will never use the Whole 40GB , let 's say it will use 15 GB, then the rest of the space (25GB) will never be used by other VMs, since its already allocated.. ?

OR I misunderstood the concept of Thin Disk

Probably, the 40GB is the limit that the Thin Disk can use..and in the mean time if other VMs use all the space on the Datastore where that VM (that has thin disk) on, then the VM will not get to 40GB of usage..since the space could have been used by other VMs ?

any clarification  ?

Thank you
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Question by:jskfan
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Qlemo earned 280 total points
ID: 41856049
"Allocated" doesn't really fit with Thin  Provisioning. Your 40 GB are only allocated if you really use them by filling up the disk with 40 GB of data. And once you did that, it remains at 40 GB, even if you delete all files.

Thin Provisioned disks may extend to the size you provided, but will only be as large as needed. The "free", unallocated space can be used by other VMs. So you can buld up 10 VMs with 500 GB thin p. disks on a 500 GB partition, as long as you do not really make use of the virtual disk space. If one of the VMs fills up its disk, others won't be able to allocate more space, and fail (i.e usually crash in some way).
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by:jskfan
ID: 41856099
when you create new VM and assign a size to the disk (I guess it is called provisioning).
well if the Vm has used 15gb out of 40GB, and all other VMs in the same datastore run out of space and need more.
Will they be able to use the 25GB left from not being used by the VM you created ?
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by:Qlemo
ID: 41856108
Yes. The 40 GB is used for overall calculation of over-provisioning (which is reasonable to a certain extend, depending on the requirements), but is not "reserved" in any way.
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by:jskfan
ID: 41856114
Means other VMs can use space  of the VM that has Thin Disk, if it has not been used yet by the VM, and other VMs need that space........Correct ?
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by:Andrew Hancock (VMware vExpert / EE MVE^2)
Andrew Hancock (VMware vExpert / EE MVE^2) earned 220 total points
ID: 41856125
Correct, but be careful, because if you overprovision and allocate more space in Thin disks, than space you have on the datastore, and ALL VMs demand that space....

the VMs will fail.

It means, that you have to be overally careful, when using thin disks, and ensuring you manage and document space requirements carefully.
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by:Qlemo
ID: 41856207
https:#a41856049 should be pretty clear about that.
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by:jskfan
ID: 41856251
Thank you for you explanation Guys
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ID: 41856264
No problems, just be careful if you use them, and manage and document them correctly, and keep an eye in and use reporting tools.

Overprovision is a big problem when using Thin disks, also some applications do not support them, e.g. Exchange.
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