Score:3

Query about Thin Provisioning and Thick Provisioning

ck flag

If i have storage LUN created as thin provisioned and mapped it to VMware Datastore. From that Datastore thick eager VMDK allocated to VM.

Does this action reserve VMDK capacity on Backend Storage and that capacity will not be available for other host for write if we have over-provisioned storage ?

vidarlo avatar
ar flag
E.g. https://blogs.vmware.com/vsphere/2014/05/thick-vs-thin-disks-flash-arrays.html will answer how ESXi handles this.
Score:5
vn flag

vSphere write whole capacity with “0” with “thick provisioned eager zeroed”. It means, that the storage on LUN should be reserved, because all of the allocated blocks are rewritten. But, if backend storage supports deduplication and/or compression, “zeroed” vmdk takes small amount of space on SAN due to extreme high deduplication ratio of “0”-blocks. So, after the writing of “real” data on vmdk, the deduplication ratio will decrease and it can be a risk of lack of storage, because of overprovisioning. Here a good article, how storage provisioning works in vSphere - https://www.vmwareblog.org/vmware-esxi-disk-provision-work-difference-one-better/

Ankit avatar
ck flag
Lets' say i have 2TB storage capacity and from that i have created three Luns to satisfy over-provisoning condition and allocated to ESXi. ThinLun1 - 1TB, ThinLun2 - 1TB, ThinLun3 - 1TB, Action 1) ThinLun1 -> Allocated to ESXi -> Created Datastore named (DS1) -> Allocated thick provisioned eager zeroed (1TB) to VM. Action 2) ThinLun2 and ThinLun3 -> Allocated to ESX -> Created Datastore (DS2) Does my Action 1 - will reserve 1TB space on storage ? other two volumes (ThinLun2 & ThinLun3 ) can only use rest of 1TB space?
Ankit avatar
ck flag
I am suspecting zero detection feature on storage will help to find zero block, if Thin Provisioned lun is allocated from storage to Datastore and thick provisioned eager zeored vmdk is allocated but not written anything on that vmdk. On storage, usage will be minimal not 1TB as Lun from storage is thin provisioned.
Score:0
bz flag

Generally storage LUNmapped to VCenter is thin provisioned, but it is highly recommended to provision thick to vm from datastore. As you are using disk from Datastore, it doesn't matter if backed lun is over provisioned or not because a monitoring agent always checks the DS health and warn if it reaches near to the threshold. From storage end as well they have many methods to check the capacity thresholds and they can easily add more storage if it reaches to actual threshold.

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