Few errors are more alarming to a VMware administrator than seeing a datastore marked as “inaccessible.” A datastore outage instantly threatens virtual machines, applications, and critical business operations.
Why it matters: when a datastore goes offline, VMs may fail to start, stop responding, or become orphaned, causing costly downtime and putting data integrity at risk. For businesses that rely on VMware infrastructure, every minute counts.
The goal of this guide is to explain why VMware datastores become inaccessible, how to identify the root cause, and what steps you can take to safely recover them without making the situation worse.
What Does “Datastore Inaccessible” Mean?
In VMware vSphere and ESXi, the term “inaccessible” means that the host cannot mount or read the datastore, even though the underlying device may still be visible. This is different from a datastore being unmounted, which is an intentional state where the datastore is disconnected but not corrupted.
When a datastore is inaccessible, the impact is immediate:
- Virtual machines may appear as “disconnected” or “orphaned.”
- Running VMs could hang or freeze.
- New tasks such as powering on or migrating VMs will fail.
Common Causes of Inaccessible VMware Datastores
VMware datastores can become inaccessible for a variety of reasons, many of which trace back to the underlying hardware or configuration. Physical problems such as RAID or disk failures, faulty storage controllers, or even loose cables and malfunctioning HBAs are frequent culprits. On the software side, issues like incorrect multipathing or zoning, misconfigured iSCSI/NFS settings, or an unclean ESXi shutdown can easily disrupt datastore access.
Corruption within the datastore itself is another common cause. Damaged VMFS metadata or a deleted partition table may prevent VMware from mounting the volume. Human error also plays a role—accidental unmounting or formatting the wrong disk can render a datastore unreachable. Finally, external factors such as sudden power loss during write operations or mismatched firmware and driver versions between storage and host can also lead to datastore inaccessibility.
Recognizing the Symptoms
When a vmware datastore inaccessible, the signs are usually hard to miss. In vSphere or ESXi, the datastore itself will be flagged as “inaccessible,” and any virtual machines stored on it may refuse to power on, shut down, or migrate. Administrators digging into ESXi logs—such as vmkernel.log or hostd.log—often find recurring I/O errors pointing to deeper storage issues.
Command-line tools can provide further evidence, with utilities like esxcli or partedUtil reporting missing or unreadable partitions. On the performance side, affected systems may experience stalled tasks, degraded I/O throughput, or VMs freezing altogether. These red flags typically indicate that immediate investigation is required before the problem escalates into potential data loss.
Initial Safety Precautions Before Fixing
Before taking action, it’s essential to avoid making the situation worse:
- Stop all write operations to the affected datastore immediately.
- Document the environment (datastore UUID, VMFS version, ESXi build, storage model).
- Disconnect the datastore from production workloads to prevent accidental writes.
- Clone or image the disks using dd, Clonezilla, or enterprise-grade tools.
- Work on copies only, leaving the original untouched.
Step-by-Step Recovery Tips and Fixes
Step 1: Verify Hardware and Connectivity
- Inspect RAID health and SMART status.
- Review controller logs for disk errors.
- Check cables, HBAs, and storage switches for faults.
Step 2: Confirm Storage Visibility in ESXi
Run:
esxcli storage core device list
to check if the device is detected.
Check multipathing with:
esxcli storage core path list
Step 3: Attempt Manual Mount
List all filesystems:
esxcli storage filesystem list
Try remounting with:
esxcli storage filesystem mount -l <datastore_name>
Step 4: Validate Partition Tables and VMFS Metadata
Check partition layout with:
partedUtil getptbl /vmfs/devices/disks/<device>
Inspect VMFS metadata with:
vmkfstools -P /vmfs/volumes/<datastore_UUID>
Step 5: Recover from Backup or Snapshot
If backups exist, restore affected VMs using vSphere Replication, Veeam, or other solutions.
Step 6: Use VMFS Recovery Tools (If Mount Fails)
Leverage third-party recovery utilities capable of scanning corrupted VMFS volumes, rebuilding metadata, and extracting VMDK files.
Step 7: Address RAID-Level Issues (If Applicable)
If the datastore relies on RAID storage:
- Rebuild or repair the RAID array first.
- Do not initialize or format the array before ensuring all data is recoverable.
Long-Term Best Practices to Prevent Inaccessible Datastores
- Maintain regular backups of VMFS datastores and VMs.
- Deploy UPS systems to prevent data loss from power outages.
- Keep ESXi hosts, storage drivers, and firmware updated.
- Monitor RAID health and replace failing drives early.
- Test datastore mounting in non-production environments.
- Use replication or stretched clusters for high-availability workloads.
Conclusion
An inaccessible datastore doesn’t necessarily mean permanent data loss. By approaching the issue methodically—checking hardware, verifying partitions, attempting safe remounts, and escalating to recovery tools only when needed—you maximize your chances of restoring access without damaging critical data.
Key takeaway: stay calm, document your environment, and always work on disk copies. With careful action, many datastore accessibility issues can be resolved without long-term impact on your VMware infrastructure.
