Coexistence of vSAN Disc Groups (PFTT=1 RAID1) & Local HDDs on RAID0/JBOD

[moazanjum01]

Hi everyone,

Need help to achieve following scenario

I have 3 hosts with vSAN Configured with RAID0 PFTT0, having enough space so that RAID1 can be applied on those VMs which need performance & Availability.

Is it possible to make 2 vSAN disc groups within vSAN

Apply RAID1 policy on all VMs with PFTT=1

& after this configuration perform storage vMotion to a DAS/ or local HDDs for all those VMs which only require capacity & can manage availability by themself.

Then evacuate some discs from vSAN & make RAID0/JBOD from physical controller (model: HPE p816i-a sr)

Then perform storage vMotion back to local RAID0 volume again.

Final Shape of environment:

Now, high performance VMs are running on vSAN with 2 DGs configured, discs pass-through via same controller. SPBM = RAID1 & PFTT=1

          Other VMs running on local RAID0 datastore (RAID0 configured via same RAID Controller)

Is it doable?

Regards,

Moaz Anjum

[TheBobkin · Accepted solution]

Hello Moaz,

While it might be technically feasible, this is a bad idea and is thoroughly unsupported - what this means is that when/if it breaks you are taking full responsibility for fixing and supporting it:

IO Controller Mode	Drive Assignments	vSphere supported?	vSAN supported	Caveats
Mixed	Some devices assigned as single drive RAID-0, some as raw (Passthru) HBA devices	Yes	No, Untested	All the devices must be assigned for vSphere usage regardless of mapping as RAID or non-RAID. Be careful not to create an imbalance in your storage as RAIDed devices may exhibit a different performance profile that Passthru/HBA ones

VMware Knowledge Base

• Do not mix the controller mode for vSAN and non-vSAN disks.
  • Mixing the controller mode will mean that various disks will be handled in different ways by the storage controller. This introduces the possibility that issues affecting one configuration could also affect the other, with possible negative consequences for vSAN.
  • If the vSAN disks are in pass-through/JBOD mode, the non-vSAN disks must also be in pass-through/JBOD mode.
  • If the vSAN disks are in RAID mode, the non-vSAN disks must also be in RAID mode.
• If the non-vSAN disks are in use for VMFS, the VMFS datastore should be used only for scratch, logging and coredumps.
  • Virtual machines should not be running from a disk or RAID group that shares its controller with vSAN disks or RAID groups.
  • ESXi host installation is permitted on non-vSAN disks attached to same controller.

VMware Knowledge Base

Why don't you just use a separate controller for the VMFS/JBOD?

Controllers are relatively cheap controllers and it doesn't even have to be one that is on the vSAN HCL if you are not using it for vSAN.

Bob

[moazanjum01]

First of all, thanks for your valuable feedback.

regarding the KB, before your reply my understanding was different: in case we present some drives to vSAN as Passthrough & some as RAID0 only then it is not supported with vSAN...because whole KB talks about presenting drives to vSAN & vSphere taking one scenario at a time for vSAN & then same scenario of presenting discs to vSAN.

So if in

Scenario 1: we have present drives with RAID0 & some drives as RAW TO VSPHERE ---- then it is good to go with

Scenario 2: we are going to present RAID0 drives to vSAN & simultaneously present drives (from same controller) in RAW/passthrough mode as well TO VSAN...ONLY THEN IT IS NOT

                    SUPPORTED

MY CASE: RAID0/JBOD to vSphere & passthrough to vSAN (your point also noted & I will use all disks in Pass-through/JBOD Mode for all drives) --- in my opinion, my scenario is different.

IO Controller Mode	Drive Assignments	vSphere supported?	vSAN supported	Caveats
Mixed	Some devices assigned as single drive RAID-0, some as raw (Passthru) HBA devices	Yes	No, Untested	All the devices must be assigned for vSphere usage regardless of mapping as RAID or non-RAID.Be careful not to create an imbalance in your storage as RAIDed devices may exhibit a different performance profile that Passthru/HBA ones

Separate RAID Controllers can be used & in fact it is better to use separate controllers for vSAN & vSphere.

[TheBobkin]

Hello Moaz,

Just to clarify:

"your point also noted & I will use all disks in Pass-through/JBOD Mode for all drives"

Even if you pass all disks in same mode, it is not supported to have vSAN disks and non-vSAN disks on the same controller if they are used for running VMs - this is noted in my above comment and in the 2nd linked KB.

Bob