When you use the virtual environment for your server you will also be using the virtual disk types in order to assign & use the storage for the server. So in VMware there are 3 types of disks you can assign to your virtual server at the time of creation or later. Thin Disks & Thick Disks.
When we create a vm we need to allocate some disk space to the vm for used as the storage. Disk is used from the datastore which is added into the vSphere from the Storage LUN. Storage LUN comes from the Storage Arrays or Storage Boxes.
Thin Disks :-
Thin disks are the most used disks in the virtual machine because of it’s dynamic nature. Thin disks allocates the space on the disk on demand. let say you have created vm with 10GB of Thin disk then vm will show the 10GB provisioned disk but it will use from the datastore as much required only. Let say guest os uses only 5GB of disk then only 5GB plus additional vm files such as config files,log files etc will be allocated from the datastore instead of the full 10GB disk. When you add new Thin disk it will not take the much time to add or extend the disk if compared to thick disks.
Thin disks are not recommended in some scenario where you will require the higher disk usage such as database server. In terms of performance where you require disks with higher performance thin disks are not recommended.
You can convert the Thin disk to thick disks. Advantages of using thin disks is that you can use the storage efficiently & you can save the cost of storage. Disadvantages include over commitment of storage, decrease in performance.
When you use the Thin disks you can see that there is difference between allocated size & the actual usage on the storage.
In the below example you can see that the VM assigned storage is 20GB but actual used on the storage is only 6.8GB it is because of the Thin Disks.
Thick Disks :-
Thick Provision disks as the disks when created all the disk space is allocated at the time of creation only. So if you create the virtual disk with 1TB storage then all the 1TB of storage will be allocated to the vm at the time of creation from the datastore & you can not use that space for other vm’s. There are 2 types of Thick Disks are there Thick provision lazy zeroed & Thick provision eager zeroed.
When you use the Thick disks you can see that there is whole storage is used which is assigned to the disk.
In the below example you can see that the VM assigned storage is 20GB & the used storage is also 20GB in case of Thick disks.
Thick provision lazy zeroed :-
Thick provision laze zeroed when used it allocates all the space from the datastore to the vm at time of creation only. When the disk is created it is not erased but zeroed out on demand while writing the data from the virtual machine. performance of laze zeroed
Thick provision eager zeroed :-
Thick provision eager zeroed also allocates the whole disk space at the time of creation from the datastore. When this disk is created all the data is zeroed out of the disk. This disk usually takes much longer time as compared to other disks. This disks are best in terms of performance. This disks helps in time where the vm require higher data writes. This disk support the clustering feature such as Fault Tolerance.
Advantages of Thick Disks :-
- One can not over commit the disks
- Easy to manage
- No performance overhead
Disadvantages of Thick Disks :-
- Expensive in terms of storage
- Takes time to provision.
- More Storage is required which requires additional cost.
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