cannot remove datastore because one or more virtual machines are still registered on it

[itsbonar]

I have an accident with my server storage after resolve it my host esxi inaccessible to datastore Synology. And then I will remove Datastore and rescan again but After unregister vm  I got some error

[SureshKumarMuth]

Please check if that datastore is used for HA heartbeating. 

[a_p_]

This may also be caused by one or more VMs with ISO images configured for their virtual CD-ROM that were stored on that datastore.
In such cases, make sure that the VMs' virtual CD-ROM  is not marked as connected, and set it from ISO image to Client Device.

Note that this can also  be caused by VMs with snapshots, where - at the time of snapshot creation - an ISO was attached.

André