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Yes—but an iSCSI LUN being visible to multiple hypervisor hosts does not, by itself, make it safe for them to use concurrently. Safe access depends on what you intend to share and on a supported coordination layer: for example, a shared VM datastore, a cluster-managed volume, or a guest cluster using the required disk reservations. Do not independently mount an ordinary read/write filesystem on multiple hosts unless that filesystem explicitly supports concurrent shared access.
What does “share an iSCSI LUN” mean?
An iSCSI LUN is block storage presented over a network. Several hosts may be able to log in to the target and see the same block device, but that visibility does not coordinate their writes. The safe configuration depends on the intended use:
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- Shared VM storage: Hosts access common VM files through a datastore or storage layer designed for shared use.
- Clustered host volume: Hypervisor cluster software manages ownership and concurrent access to a disk or volume.
- Shared disk inside a guest cluster: Guest operating systems arbitrate access using a supported clustering configuration, with hypervisor and storage requirements that may differ from ordinary VM storage.
- Independent mounts: Two hosts mount a regular filesystem read/write on the same LUN without shared-filesystem coordination. The platform documentation discussed here does not endorse this as safe.
In short, check the sharing mechanism—not just whether both hosts can connect to iSCSI.
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| Platform or use | Coordination layer | Important qualification |
|---|---|---|
| VMware shared VM storage | VMFS datastore | VMFS is a shared filesystem for block storage; it is not equivalent to independently mounting an arbitrary filesystem. |
| Hyper-V cluster storage | Failover clustering and, where used, Cluster Shared Volumes (CSV) | Follow the cluster workflow and ensure the intended nodes can access and own the disk. |
| VMware guest WSFC shared disk | Windows Server Failover Clustering with SCSI-3 Persistent Reservations (SCSI3-PRs) | Configuration is version-, controller-, and storage-dependent; use the applicable support guidance. |
| Proxmox VE shared LVM on iSCSI | LVM with cluster-wide locking | Proxmox documentation says LVM-thin pools cannot be shared across multiple nodes. |
Hyper-V: put the LUN under cluster management
Microsoft System Center Virtual Machine Manager (VMM) guidance treats iSCSI access as part of a cluster-storage configuration, not as permission for uncoordinated mounts. It calls for MPIO on each iSCSI host, correct initiator and session configuration, and LUN availability to the intended cluster nodes.
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- Enable MPIO on each iSCSI host. Apply the storage vendor’s recommended device-specific module (DSM) and path policy where applicable.
- Configure iSCSI connectivity. Add the target portals, log each host initiator into the array, and ensure the Microsoft iSCSI Initiator service is running and set to Automatic.
- Present the LUN to the intended nodes. For storage not managed by VMM, provision the LUN to every cluster node that needs it. In the described VMM configuration, Microsoft says each cluster node must be a possible owner of the cluster disk.
- Use the cluster’s storage workflow. The VMM guidance says to mount and format the disks on one node, then manage available cluster storage through the cluster workflow. Convert suitable available storage to CSV only as required by the design.
Changing a disk’s cluster storage state is an operational change, not a harmless toggle. Microsoft warns that converting shared storage to available storage while virtual machines are using it can cause serious data loss. Check active VM and virtual-disk use and follow the documented migration or shutdown procedure before changing state.
VMware: distinguish a VMFS datastore from a guest-cluster disk
For shared VM files, use a supported datastore
VMFS is VMware’s shared filesystem for block storage and is the relevant layer when multiple ESXi hosts need a common datastore. A LUN presented to multiple hosts should be configured as the appropriate shared datastore, not formatted as a general-purpose filesystem and mounted independently by each host.
For Windows guest WSFC disks, check the exact configuration
Windows Server Failover Clustering (WSFC) virtual machines with shared disks are a separate use case. Broadcom’s guidance identifies SCSI-3 Persistent Reservations as the mechanism for arbitrating shared-disk access and specifies version-dependent reservation, controller, storage, and placement requirements. Its Cluster-Across-Boxes (CAB) arrangement places cluster VMs on different ESXi hosts. Broadcom says Cluster-in-a-Box (CIB) should not be used in production in the cited configuration guidance; do not generalize that statement beyond its WSFC context.
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Proxmox VE: shared iSCSI does not mean every volume type is shareable
Proxmox VE distinguishes the iSCSI connection from the storage layer built on top of it. Its documentation describes iSCSI as block-level storage without a management interface, and describes placing LVM on a shared iSCSI LUN with cluster-wide locking. It also states that LVM-thin pools cannot be shared across multiple nodes.
A storage configuration marked “shared” describes an existing sharing arrangement; that setting does not create the locking or coordination that makes concurrent access safe. Proxmox also warns against using the same storage pool across separate Proxmox VE clusters: some operations require exclusive access, while the required locking works within a cluster rather than between clusters.
Checklist before connecting multiple hosts
- Name the use case: shared VM datastore, clustered host volume, or a raw disk shared by guest cluster nodes.
- Verify support for the exact combination: hypervisor and guest versions, storage array, protocol, controller, and sharing mode.
- Check presentation consistency: confirm intended host initiator identities, target mappings, and LUN visibility on every required node.
- Configure redundant paths correctly: use MPIO and vendor-recommended DSM or path settings where applicable; multiple paths do not replace cluster coordination.
- Use the right coordination layer: shared datastore, cluster volume and locking, or guest-cluster reservations as required by the design.
- Review failure and recovery operations: understand ownership, node loss, path loss, backup coverage, and how to restore the cluster configuration. Redundancy and clustering are not backups.
- Plan storage-state changes: verify no VM or virtual disk is still using a volume before changing its cluster role, following the platform’s procedure.
What to compare when choosing a shared-storage design
Compare supported operating modes rather than treating the choice as simply iSCSI versus another transport. Confirm how each candidate handles coordination and guest workloads, whether the release and array combination is supported, and what happens during path, controller, or host failure. Also check operational needs such as snapshots, clones, live migration, and management workflows; capabilities vary by storage backend and platform.
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