Storage DRS generates only one datastore as initial placement recommendation in clusters with physical RDM

Products

• VMware vSphere ESXi

Issue/Introduction

Symptoms:

• Storage DRS generates only one datastore as placement recommendation when creating Virtual Machines in SDRS clusters with physical RDMs.
• Always chooses the same datastore and does not provide any alternative recommendations.
• Datastore belonging to the affected SDRS cluster has Physical RDM pointer files.

Cause

When an RDM is created, it creates a mapping file with the extension -rdmp.vmdk with size equal to the size of RDM disk/LUN. When SDRS calculates the committed disk space for all the VMDKs present on the datastore, it treats this mapping file also as a virtual disk for the VM. However, this mapping file size will not be calculated while calculating the datastore disk space usage due to which the UI does not show RDM disk size consumption.

SDRS takes into consideration the size of RDM during load-balancing as if it were to move the disk to another datastore, the -flat disk will be of size of RDM. Therefore, if the ratio of demand/capacity is going beyond 1 as per the preceding calculation, SDRS recommends and forcefully displays the best suitable datastore for creating a new virtual machine.

Resolution

This is a known issue affecting vCenter Server 5.5, 6.0 and 6.5.

Currently, there is no resolution.

To work around this issue, use one of these options:

Caution: Down time is required for the virtual machines that have RDM disks mapped to it.

• Store all the RDM mapping files on a dedicated datastore outside the cluster.
• Remove any datastore that is having a RDM pointer file from the SDRS cluster.

Additional Information

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