Is THICK LUNS and THIN VMDK's a good provisioning strategy?

JB Blanco
JB Blanco used Ask the Experts™
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Thick LUNS and THIN VMDKs

This is how this new environment ive just acquired last month has all their storage setup.

They are using all THICK LUNS at the Array/Block level,  and THIN at the VMware level.

Is this a good idea?  best practices?  

I would like to hear your thoughts

Here is our SAN and VMware environment details:

SAN = all Fibre chanel EMC Unity550F's  All Flash SAS Flash 4

VMware= Vcenter 6.5 10000 Build 6816762
Esxi hosts = 5.0, 5.5, 6.0, and 6.5

The EMC Unity550F's have capability  profiles for VVols but we are not using them.
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nociSoftware Engineer
Distinguished Expert 2018

Commented:
It all depends on how do you expect your systems to FAIL.....
in this case on storage demand....
a) Just hang (block while the host or SAN is attempting to enlarge the volume)
  any OS system expects  that it can use all the space that is allocated to it. (you gave mandate for that to the system by telling the Disk size...).
b) The system should continue to work (albeit more slowly because the storage allocation requests might fail after a some time).

Overallocating storage might be a viable solution to storage demands f.e with test systems that live for a short while.
  (same like a airlines book more passengers then they have seats for..., assuming there are some no-show's anyway).
If running mission critical systems like one controlling a Nuclear Reactor, or some critical process in a chemical plant or Airtraffic control "this might not be the best idea"(tm).

So it depends..., How and where do you want your failure impact.
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017
Commented:
I don't see a problem, providing reporting and managing storage is okay!!!

e.g. don't over provision storage!

I think you've got more issues with support and 5.0 and 5.5, than worrying about storage at present!
JB BlancoSr Systems Engineer

Author

Commented:
So what if we did everything Thin?

Thin on the storage array and thin in VMware?
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nociSoftware Engineer
Distinguished Expert 2018

Commented:
Thin Storage is a way of overbooking/overcommitting on storage.

Say you have 1TB of storage and want  to have 50GB sized disks...
that would set the limit to 20 disks.   (without risk of blocking on extending disks in the storage server).
(This is THICK provisioning  from the storage system).

Now if you want > 50 system you can opt for THIN disks on storage say on avarage only 20G of the 50G is used on each disk.
so you could accomodate 40 of such disks..., and now a change is done that all disks require 30GB on avarage....
The SAN storage will be depleted.  and several VM's will get strung out waiting for expansion....

So THIN provisioning from STORAGE is a risk that needs managing, and you need to determine if that risk is worth while.
(Any form of over committing will hold a risk for depletion of the resource, like i say before: to some extend airlines are thin provisioning their planes  they sell more seats then they actually have and hope not all passengers show up at the check-in).
JB BlancoSr Systems Engineer

Author

Commented:
Thin Storage is a way of overbooking/overcommitting on storage.

Say you have 1TB of storage and want  to have 50GB sized disks...
that would set the limit to 20 disks.   (without risk of blocking on extending disks in the storage server).
(This is THICK provisioning  from the storage system).

Now if you want > 50 system you can opt for THIN disks on storage say on avarage only 20G of the 50G is used on each disk.
so you could accomodate 40 of such disks..., and now a change is done that all disks require 30GB on avarage....
The SAN storage will be depleted.  and several VM's will get strung out waiting for expansion....

So THIN provisioning from STORAGE is a risk that needs managing, and you need to determine if that risk is worth while.
(Any form of over committing will hold a risk for depletion of the resource, like i say before: to some extend airlines are thin provisioning their planes  they sell more seats then they actually have and hope not all passengers show up at the check-in).

Thanks for the explanation, I understand that.  So by using THICK on the Storage array, I am provisioning all the available block storage upfront.   And then if I choose THIN on the VMware VMDK Settings, I am only using the available space that I need for the VMDK.  So does this makes sense?  Is it beneficial doing it this way?
Top Expert 2016

Commented:
Thick on SAN, Thin on VM's is also how i'd do it.
Software Engineer
Distinguished Expert 2018
Commented:
Provisioning  Think on SAN save a lot of headaches and prevents a lot of obscure failing modes.  Thin provisioning on VM gives more insight in actual usage of storage without diving into each system. (not sure if it makes a difference for temporary snapshots though).

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