Two-Node Hyper-V Failover Cluster Part 5 of 15: Add 500GB VHDX to the iSCSI VM

The iSCSI VM has its OS disk (40 GB) but nothing to share yet. This part adds a 500 GB Fixed VHDX as the storage pool, attaches it to the VM, brings it online in the OS, formats as NTFS, and mounts as D:. In Part 7 we’ll carve this disk into iSCSI LUNs (Quorum, Data, etc.) for the cluster.

Hyper-V side — create + attach the VHDX

Hyper-V Manager right-click context menu on the iSCSI VM showing Settings, the entry to add a new virtual hard disk — On the Hyper-V host: right-click the `iSCSI` VM > **Settings**.

Hyper-V Manager > right-click iSCSI VM > Settings.

VM Settings dialog with SCSI Controller selected and Hard Drive being added on the right side — SCSI Controller > Hard Drive > Add.

SCSI Controller > Hard Drive > Add.

Hard Drive properties pane with the New button being clicked to launch the New Virtual Hard Disk Wizard — Hard Drive properties > **New** to launch the wizard.

Click New to launch the New Virtual Hard Disk Wizard.

New Virtual Hard Disk Wizard Before You Begin step — Before You Begin — Next.

Before You Begin: Next.

Choose Disk Type step with Fixed Size selected for consistent IOPS and no expand-pauses during workload — **Fixed Size**. Pre-allocates the entire file. No expand-pauses during workload. Consistent IOPS.

Fixed Size. This is the load-bearing decision in this part. Fixed pre-allocates the entire 500 GB on host disk — takes longer to create (10-30 min) but the file is fully laid out and never has to expand mid-workload. Dynamic VHDX would expand on demand, causing IO pauses every time it grows.

Production rule: SAN backing storage is always Fixed. Dynamic is for lab convenience or short-lived VMs. Cluster storage = Fixed, no exceptions.

Specify Name and Location step with the new VHDX file being named (e.g. iSCSI-Storage) — Name: `iSCSI-Storage.vhdx` (or similar). Default location is fine for lab.

Name: iSCSI-Storage.vhdx. Location matters — put this on the fastest physical disk on your host. The entire cluster’s storage performance depends on this single VHDX. If it’s on slow spinning disk, the cluster is slow. If on NVMe, it’s fast.

Configure Disk step with the size set to 500 GB, sufficient for the cluster LUNs in upcoming parts — **Size: 500 GB**. Enough for the cluster’s LUNs we’ll create in Part 7.

Size: 500 GB. Enough for the cluster LUNs (Quorum 1 GB + Data 100 GB + headroom for growth/extra LUNs).

Wizard summary screen showing all selections ready to commit — Review and Finish.

Review.

New Virtual Hard Disk creation in progress with the Fixed allocation taking time as the entire 500 GB is pre-allocated on disk — Creation runs. Fixed allocation of 500 GB takes 10-30 min depending on host disk speed. Coffee.

Creation runs. Get coffee. The progress bar slowly fills as the host writes 500 GB of zeros to disk.

VM Settings dialog Apply button being clicked to attach the newly created disk to the iSCSI VM — Apply > OK on VM Settings to attach the disk.

Apply > OK on VM Settings to attach the new disk to the iSCSI VM.

Guest OS side — bring online + format

Server Manager on the iSCSI VM with File and Storage Services > Disks pane showing the new disk listed as Offline” /><figcaption>In the iSCSI VM: Server Manager > FSS > Disks. New Disk 1 appears as <strong>Offline</strong>.</figcaption></figure>
<p>In the iSCSI VM: Server Manager > <strong>File and Storage Services</strong> > <strong>Disks</strong> pane. The new Disk 1 appears as <strong>Offline</strong>.</p>
<figure class= — Right-click Disk 1 > **Bring Online**.

Right-click menu on Disk 1 with Bring Online highlighted — Right-click Disk 1 > **Bring Online**.

Confirmation dialog asking to confirm bringing the disk online — Yes to confirm.

Right-click Disk 1 > Bring Online > Yes.

Right-click menu on Disk 1 with New Volume option selected to launch the New Volume Wizard — Right-click again > **New Volume** to launch the wizard.

Right-click again > New Volume to launch the wizard.

New Volume Wizard Before You Begin step — Wizard start.

Server selection step ensuring Disk 1 is the target — Server selection — this VM.

Disk selection step confirming the new 500 GB disk — Disk: the new 500 GB disk.

Wizard: server, disk — just confirm the new disk is selected.

Volume size step accepting the default size which uses the entire 500 GB minus formatting overhead — Volume Size: accept default (uses full disk).

Volume Size: accept default. Uses entire 500 GB minus a few MB of NTFS overhead.

Drive letter assignment step with D: selected as the new volume letter — Drive Letter: `D:`.

Drive Letter: D:.

File system settings step with NTFS selected, default allocation unit, and a meaningful volume label like iSCSI_Storage_500GB — File System: **NTFS**. Default allocation unit. Label: `iSCSI_Storage_500GB`.

File System: NTFS. Default allocation unit (4 KB). Label: iSCSI_Storage_500GB — meaningful labels save lives during 03:00 troubleshooting.

Review.

Volume creation completed dialog with all steps showing green ticks — Created.

Volume created.

File Explorer on the iSCSI VM showing the new D: drive present with ~500 GB free, ready to host the iSCSI Target’s LUNs in Part 7 — `D:\` drive present in File Explorer with ~500 GB free. Ready to host the iSCSI Target’s LUNs in Part 7.

File Explorer confirms D:\ with ~500 GB free. Ready for Part 7 to lay down iSCSI Target LUN files here.

Things that bite people in this part

VHDX on slow host disk

The iSCSI VM’s data VHDX IS the cluster’s storage. If you put it on a USB drive, the cluster runs at USB speed. Plan disk placement — this single file determines cluster performance.

Dynamic chosen by accident

Default selection in Hyper-V wizard varies. Always explicitly select Fixed for cluster-relevant storage.

Insufficient host space

Fixed 500 GB needs 500 GB free on the host disk. If you don’t have it, creation fails partway through. Check capacity before starting.

Drive letter conflicts

If D: is already in use (e.g., the OS image was mounted there), the wizard offers the next free letter. Either accept or remove the existing D: assignment first.

Forgot NTFS

The wizard offers ReFS (Resilient File System) as an option in Win Server 2022. ReFS is great for some workloads but iSCSI Target VHDX files prefer NTFS for compatibility. Stick with NTFS.

What’s next

Part 6 creates the three Hyper-V virtual switches (External, Storage, Heartbeat) and attaches them to the VMs — the network plumbing the cluster needs. See the full series at Hyper-V Failover Clustering pathway.

Tags: #Disk Management #Failover Cluster #Hyper-V #iSCSI #VHDX