what is difference between deup&compression in vsan data service and vSAN policy

[baber]

In vSAN7 there are 2 options to enable dedup and compression the first one according to pic1 is when we want to enable vSAN in data service  and the second is when want create  a policy . I know the second is for while we want assign this policy for specific vm but

1- when we use the first option in data service ?

2- can  we disable dedup and compression in data service when want enable vsan and just enable it in policy and use for specific vms ?

3- what will happen if we just enable it in the data service and not select dedup and compression due create new policy ?

[TheBobkin]

@baber Actually the second isn't an option to enable either of these services - Storage Policies are now more granular in which clusters they are compatible with based on features (e.g. dedupe&compression) and configuration (Hybrid, All Flash etc.) but selecting this in a policy obviously won't enable these on a cluster (nor magically transform Hybrid into All Flash), just make whatever clusters don't match these show as incompatible.

[baber]

1- Is that your means wile we are using AFA if want use dedup and replication it is mandatory to enable dedup& replication in the data services ?

2- if I just enable dedup&replication in the policy and not in the vsan services it will not work is that correct ?

3- If we enable dedup&replication in vsan services but due create vsan policy not enable dedup & replication will it apply or we have to enable dedup & replication in two steps?

4- for example I was run vsan 6 months ago without enable dedup and replication in vsan services and if enable it for today will it dedup and compress new data or also can aply for previous data ?

[TheBobkin]

1. Yes.
2. Correct, and even more so, it won't show any vsanDatastores that have that feature disabled as compatible and won't be able to use them with that policy.
3. Dedupe&Compression isn't actually applied at the policy level - any data placed on a D&C/Compression-only enabled vsanDatastore will have those features applied to their data (regardless of what is in their policy).
4. If you enable D&C/Compression-only on a cluster it will do a rolling reformat of all Disk-Groups and all data, all data will be recreated, not just new data.

[baber]

1 - So if I want to apply dedup and compression just enable it on the vsan data service and no need to enable it due create policy is that correct ? If the answer is Yes want to know why VMware place this option due create policy ?

2- You said if I enable dedup and compression in vsan data service after 2 months that vSAN run it will be also dedup and compression on previous data so will data intact or will format vSANDatastore ?

[TheBobkin]

1. As I said above, D&C is applied on the Disk-Group (and enabled on the cluster) level only - As I also said above, these options were added for more granularity as Storage Policies are vCenter entities and don't belong to any one vSAN cluster and were added with remote-vsanDatastore feature.

2. No, I said "reformat of all Disk-Groups and all data" - this means it will do move all data off Disk-Groups (one at a time), recreate the Disk-Group in new dedupe-enabled format and then continue to do this for all remaining Disk-Groups in a rolling manner. Do note that this is (fairly obviously) resource-intensive and should be done in relatively quieter business hours and depending on the footprint, performance and contention of the storage resources of the cluster can take quite a long time (e.g. up to many days).

[baber]

Thanks. Would you please say exactly when we must select D&C in the policies ? When that is mandatory ? would you please give an example ?

[TheBobkin]

I don't really see any reason where it would be mandatory, it is more so a guardrail so that only the datastore with the features that one wants to be used are shown as compatible/available without having to check/know the configuration characteristics of every cluster.

The only example I can think of where it might be 'mandatory' is if datastores were being served to a client with some SLA of D&C/C-only and being able to validate this is available (e.g. where they have no access nor control of the cluster backing that datastore).

[baber]

I didn't run HCI mesh but I read while we want to use HCI mesh that is mandatory ? Is that correct ?

[baber]

As dedup &compression apply on disk group so we cannot enable/disable it for specific VMs . Is that correct?

[depping]

correct, it can only be enabled for the full datastore and not for individual  VMs.

[baber]

1- If we use HCI mesh for remote datastore we cannot enable dedup & compression on that datastore through vSAN and had to enable it previously on that traditional storage . Is that correct ? 

2- this dedup & compression policy is just a UI flag and not do specific function . is that correct ?

[depping]

1) not sure what you mean

2) the dedupe and compression policy option, as stated above, is a switch that enables vSphere during VM provisioning to only show the datastores which have that feature enabled. So if you have it set to "dedupe and compression" enabled then during VM provisioning only those datastore are shown as compatible.

[baber]

About my first question . imagine we have two remote datastore and both of them has created on traditional storage so we cannot use vsan deup & comp feature on these datastores and had to enable this feature previously on traditional stotage . Is that correct ?

[depping]

No that is not correct, the policy capabilities we are discussing are VSAN capabilities, they have nothing to do with traditional datastores. Traditional datastores would always be incompatible as they can never provide the requested vSAN features.

[baber]

Thanks. But due create vSAN in one cluster finally we have just 1 datastore (vSANDatastore) and if that is AFA can support dedup&comp and if that is Hybrid cannot support dedup&comp  . So There are not more than 1 datastore to define which one is support dedup&comp and which one not support for provision VM. I think that option due create policy ( dedup & comp) is useful while we have more than one datastore in vSAN . Is that correct ? 

[nachogonzalez]

Hi hope you are doing fine

the first option will enable Dedupe and Compression for all the vSAN objects at rest. Meaning, once they reside on disk.
The second option allows you enable on a per VM basis. Deduplication, compression and encription. EDIT: Thhis is not correct
One good use case for this is VDI: Maybe you don't want all your vSAN datastore to have deduplication and compression enabled. But for the VDI VMs you want to enable it. 
For different workloads you will have different storage policies: (your most crritical DB shouldn't have the same storage policy as the server you deployed for a test and forgot to delete).

Hope that works.

[baber]

This is not correct because dedup and compression just can enable on Diskgroup so you cannot use dedup & compression per VM 

[depping]

Dedupe and compression, and compression only, both are enabled on the vSAN Datastore level!

[nachogonzalez]

My Bad, thanks for the update.