Thin-on-thin

Pouzivat thin VMDK disk na thin provisioningu na urovni diskoveho pola?
VMware hovori "You can..."

Tu je dalsi prispevok:
So… What’s right - thin provisioning at the VMware layer or the storage layer? The general answer is that is BOTH.

If your array supports thin provisioning, you’ll generally get more efficiency using the array-level thin provisioning in most operational models.

1. If you thick provision at the LUN or filesystem level, there will always be large amounts of unused space until you start to get it highly utilized - unless you start small and keep extending the datastore - which operationally is heavyweight, and general a PITA.
2. when you use thin provisioning techniques at the array level using NFS or VMFS and block storage you always benefit. In vSphere all the default virtual disk types - both Thin and Thick (with the exception of eagerzeroedthick) are “storage thin provisioning friendly” (since they don’t “pre-zero” the files). Deploying from templates and cloning VMs also use Thin and Thick (but not eagerzeroedthick as was the case in prior versions).
3. Thin provisioning also tends to be more efficient the larger the scale of the “thin pool” (i.e. the more oversubscribed objects) - and on an array, this construct (every vendor calls them something slightly different) tends to be broader than a single datastore - and therefore more efficiency factor tends to be higher.

Obviously if your array (or storage team) doesn’t support thin provisioning at the array level – go to town and use Thin at the VMware layer as much as possible.

What if your array DOES support Thin, and you are using it that way - is there a downside to “Thin on Thin”? Not really, and technically it can be the most efficient configuration – but only if you monitor usage. The only risk with “thin on thin” is that you can have an accelerated “out of space condition”.

Zdroj:
Prvy odstavec na strane 11 VMware dokumentu
Performance Study of VMware vStorage Thin Provisioning
www.vmware.com/pdf/vsp_4_thinprov_perf.pdf

Thin on Thin? Where should you do Thin Provisioning – vSphere 4.0 or Array-Level?
http://virtualgeek.typepad.com/virtual_geek/2009/04/thin-on-thin-where-should-you-do-thin-provisioning-vsphere-40-or-array-level.html