vCenter Server applies storage filters to prevent undesirable LUNs to be displayed during the storage operation. For example if a LUN is used for RDM, a LUN will not be displayed in the list of available LUNs when you try creating a new VMFS Datastore. I cannot find or think about any use case of disabling these features but it can be tested in VCAP exam.
The type of vCenter Storage Filter (Extracted from vSphere Storage ESXi 5.0, vCenter5.0)
| Filter Name | Description | Key |
| VMFS Filter | Filters out storage devices, or LUNs, that are already used by a VMFS datastore on any host managed by vCenter Server. The LUNs do not show up as candidates to be formatted with another VMFS datastore or to be used as an RDM. | config.vpxd.filter.vmfsFilter |
| RDM Filter | Filters out LUNs that are already referenced by an RDM on any host managed by vCenter Server. The LUNs do not show up as candidates to be formatted with VMFS or to be used by a different RDM. If you need virtual machines to access the same LUN, the virtual machines must share the same RDM mapping file. For information about this type of configuration, see the vSphere Resource Management documentation. | config.vpxd.filter.rdmFilter |
| Same Host and Transports Filter | Filters out LUNs ineligible for use as VMFS datastore extents because of host or storage type incompatibility. Prevents you from adding the following LUNs as extents:
|
config.vpxd.filter.SameHostAndTransportsFilter |
| Host Rescan Filter | Automatically rescans and updates VMFS datastores after you perform datastore management operations. The filter helps provide a consistent view of all VMFS datastores on all hosts managed by vCenter Server. NOTE If you present a new LUN to a host or a cluster, the hosts automatically perform a rescan no matter whether you have the Host Rescan Filter on or off. | config.vpxd.filter.hostRescanFilter |
Testing vCenter Server Storage Filter
I have 2 ESXi Server Cluster and 3 iSCSI LUNs that are already formatted as VMFS.
Host Rescan Filter
First I will demonstrate Host rescan Filter. With the default behaviour vCenter server make all ESXi server in the cluster to rescan storage if one of the ESXi Server performs a storage operation. Let’s examine the default behaviour.
If I delete VMFS-03 Datastore from esxi-01 server, esxi1-02 will automatically rescan the storage so that both server will have consistent view of Storage.
On esxi-01 Server. I have deleted VMFS-03 Datastore.
On esxi-02 server. The server has initiated rescan as soon as I deleted VMFS-03 from esxi-01 server so both servers have consistent view of storage.
Now let me disable Host Rescan Filter. To do so, you need to go to Administration > vCenter Server Settings. Then Select Advanced Settings
On the right side bottom, enter config.vpxd.filter.hostRescanFilter with Value false, then click Add. This will disable Host Rescan Filter. You will not need to restart ESXi Servers to changes to take effect.
Then I created a new VMFS Datastore and named it New-VMFS-03 on esxi-01 server.
Then take a look at esxi-02, you won’t see NEW-VMFS-03 on esxi-02 as esxi-02 has not yet performed rescan.
VMFS Filter
Next I will demonstrate you VMFS Filter. With the default Behaviour your will not see LUNs that are already formatted as VMFS by the other Host when you try creating a new VMFS Datastore to avoid Datastore corruption.
In my Lab environment, I have iSCSI LUN9 used for NEW-VMFS-03 as I demonstrated in Host Rescan Filter. Although esxi-02 do not have NEW-VMFS-03, vCenter server is aware that LUN9 is already a Datastore and should not be formatted as a new Datastore. In order to demonstrate this, Host Rescan Filter needs to be set to false, as esxi-02 host will automatically rescans the storage as soon as I create a new Datastore in esxi-01 if Host Rescan Filter is enabled.
On esxi-02 server, if I try adding a new Datastore, I don’t see any available LUNs as vCenter server filters all LUNs used for VMFS Datastore by other ESXi host.
To disable VMFS Filter, enter config.vpxd.filter.vmfsFilter and set Value to falsein vCenter Advanced Settings.
Now if I try adding a new VMFS Datastore on esxi-02, I can see LUN9 displayed as an available LUN for a new Datastore although it is already a VMFS Datastore (NEW-VMFS-03)
RDM Filter
Third vCenter Storage Filter I will demonstrate you is RDM Filter. The RDM Filter hides LUNs from hosts if they are used for RDM. To demonstrate this, I made a VM that uses RDM called RDM-VM. LUN0 is used for this RDM hard drive.
if I tried to make a new datastore, they will be no LUNs available as LUN0 is used by RDM.
to turn off RDM Filter, enter config.vpxd.filter.rdmFilter Key and set the value to false in vCenter Advanced Settings.
Now if I try adding a new Datastore, LUN0 is visible.
Same Host and Transports
the last vCenter Storage Filter that I want to demonstrate is Same Host and Transports Filter. Same Host and Transports Filter hides incompatible LUNs when you try adding an extent to the existing Datastore. For some reason, I couldn’t make this work. In theory if I disable Same Host and Transports Filter, iSCSI LUNs should be displayed as candidates LUNs if I tried to add an extend to Local Disk based Datastore.
To turn off Same Host and Transports Filer add config.vpxd.filter.SameHostAndTransportsFilter key and set Value to falsein vCenter Server Advanced Settings.
I will update this as soon as I find out how to demonstrate Same Host and Transports Filter.
Summary
vCenter Server Storage Filter is a useful feature and it is enabled by default. I cannot think any use case why you should turn off these filters, except for Host Rescan Filter (To prevent large number of host initiates Storage Rescan at any storage operation). Well that’s why it is in the advanced settings, I guess.