Thick vs Thin provisioning

[pnorthpm]

Hello All,

Let me start off by saying this is a great forum and everyone here has had some great feedback.

I have a new environment that I am using to migrate our VM's off of older ESX servers.

The VM's that were created originally have been given very large disk sizes (100G) and are only using between 15-40Gb of space.

Some people here have had a bad experience with thin in the past because they ran out of space and the system crashed, but I don't think anyone was really keeping an eye on any systems space.

I have decided to use Thin on some of the VM's that I am V to V'ing over from the old ESX servers to help reduce space used.

Here are my questions

1.  If I thick provision some VM's and Thin provision others, even if for some reason we run out of space will the thick provisioned VM's be effected??

2.  If I enable SDRS and create a cluster of datastores will VM's automatically storage vmotion to a datastore with available space in the event a datastore starts to fill up??

3.  Can I use Storage Vmotion to change from THICK to THIN if needed??

What is the general consensus with Thin provisioning?? how many people here use Thin vs Thick??

Currently we have a 2 node DL360 cluster using HPE VSA to create a virtual SAN using the internal Drives in the DL360's.

[Finikiez · Accepted solution]

Hi!

1.  If I thick provision some VM's and Thin provision others, even if for some reason we run out of space will the thick provisioned VM's be effected??

Generally speaking - no.

However there could be some details. For example if you have a lun connected from NetApp storage, LUN will be offlined from storage side when it runs out of space.

2.  If I enable SDRS and create a cluster of datastores will VM's automatically storage vmotion to a datastore with available space in the event a datastore starts to fill up??

It depends on how you will configure SDRS automation level. There are two types - manual and fully automated. If you configure fully automated method, then SDRS will re

3.  Can I use Storage Vmotion to change from THICK to THIN if needed??

Yes, you can.

[pnorthpm]

Thanks again for your quick reply

one more question

Can I enable SDRS and create a storage cluster without causing any downtime?

we have running VM's and I don't want to do anything that may cause an outage

thanks

[emanueleroserba]

You can add already populated (and in use) datastores to a Storage Cluster..

Be aware that some situations (eg. adding a nearly full datastore and an empty datastore to the same Storage Cluster) could lead, based on sDRS settings, to a lot of storage migrations triggered, to avoid network congestion etc. better having automation level set to manual in the datastorre adding phase and apply reccomendations off peak hours, as soon as you have a balanced situation you can move to fully automated.

Ciao, e.

[pnorthpm]

Excellent,

our datastores are about equal now using about 60% of their cap.

Thank You.

[pnorthpm]

One more question sorry

So lets say I thin provision a VM that has 100G allocated to it, can that VM grow beyond the 100G it has allocated if it is thin provisioned??

Just want to cover all my bases

thanks again

[Finikiez]

No.

If you made 100Gb thin provisioned disk it can't grow beyond this size.

[pnorthpm]

Is their any way to make sure a group of servers have more privileges than others to prevent this from happening ?

maybe utilizing resource pools??

We have alerts implemented in case file systems fill up, but I would like to make sure I do everything possible to keep my production server up and running.

[Finikiez]

You can reserve space only by using thick disks no other methods exist.

You should also keep in mind the following things:

- if you take snapshots, they occupy disk space as well. Initially delta disk size is 16Mb and it will grow when you write new data in VM.

- by default thin disks only grow in size. If you delete something inside guest OS thin vmdk disk on datastore won't shrink automatically. There are additional requirements to make this possible. Read this article for example Direct Guest OS UNMAP in vSphere 6.0 | Cody Hosterman  and there was a bug in ESXi 6.5 https://kb.vmware.com/s/article/2150591

Also I don't know what storage array you use but check if you have thin or thick luns configured on your storage side.

If you have thin luns on storage keep an eye on them as well.

[pnorthpm]

Thanks so much for getting back to me

We are using HPE VSA to create a virtual SAN using the internal drives.

they are thick provisioned on the SAN side.

most of our guests are RHEL 5 servers so it's linux, I think the bug pertains to Windows 2012.

this was really helpful and I really appreciate it.