Uninterrupted operation in virtualization infrastructures is the most fundamental cornerstone of business continuity. However, the "Datastore Inaccessible" error is one of the problems that system administrators fear most and require urgent intervention in VMware vSphere environments. When a datastore becomes inaccessible, all virtual machines (VMs) running on that datastore hang, disk write/read operations stop, and serious data loss or downtime risks arise.
In this guide, we will analyze the underlying causes of datastore access problems in VMware ESXi hosts and explain how to solve this critical problem step by step.
Why Does a VMware Datastore Become Inaccessible?
A datastore becoming inaccessible is usually caused by a disconnection of the communication channel between the ESXi host and the storage unit. This situation is examined under two main headings in VMware terminology:
- APD (All Paths Down): This is the loss of all physical paths from the ESXi host to the storage device. However, the host tries to keep the paths open, hoping that the device will return. It is usually seen during temporary network outages or switch problems.
- PDL (Permanent Device Loss): This is the notification to the ESXi host that the storage device is permanently lost. It is triggered in case of LUN deletion on the storage side, authorization (LUN masking) error, or a hardware failure.
Apart from these two situations, fiber optic cable failures, iSCSI network outages, storage controller lockups, or incorrectly configured zoning operations can also completely cut off datastore access.
Step-by-Step Datastore Inaccessible Troubleshooting Path
When you encounter an inaccessible datastore, you need to follow a systematic analysis order to solve the problem.
1. Physical and Network Layer Controls
Determining whether the problem is hardware or network-related is the first step.
- Connection Protocol Audit: Whichever of the FC (Fibre Channel), iSCSI, or NFS protocols you use to connect to the storage unit, check the relevant switch and cable connections.
- iSCSI Target Ping Test: If you are using iSCSI, connect to the ESXi host's CLI interface via SSH and verify that you can ping the storage target IP addresses:
vmkping -I vmkX [Storage_Target_IP] - Zoning and LUN Masking Controls: Ensure that the relevant LUN on the storage side continues to be presented to the ESXi hosts and that zoning rules are active on the FC switch.
2. Storage Rescan on ESXi Host
After a temporary outage in the connection paths is resolved, a storage scan must be triggered for ESXi hosts to detect the new state.
- Select the relevant ESXi host in the vSphere Client interface.
- Go to the Configure > Storage > Storage Adapters tab.
- Click the Rescan Storage button to rescan both storage adapters and VMFS file systems. This process will return the datastore to "Normal" status in temporary APD situations.
3. Detailed Log Analysis with CLI
If the datastore still appears inaccessible from the interface, examining the ESXi host's log files allows you to make a definitive diagnosis.
- Connect to the ESXi host via SSH and monitor the
/var/log/vmkernel.logfile in real-time:tail -f /var/log/vmkernel.log | grep -i -E "apd|pdl|lost" - Search for "Hostd: [APD State]" or "Permanent Device Loss" in the logs. If you receive a PDL warning, you must urgently check the LUN configuration and permissions on the storage side.
4. Checking the Status of Virtual Machines
When the datastore is inaccessible, VMs running on it may fall into "Inaccessible" or "Orphaned" status.
- If the VMs do not recover automatically after the datastore connection is back, right-click the VM and use the Register or Reload options.
- If necessary, remove the virtual machine from the inventory (Remove from Inventory) and add it back to the inventory from the
.vmxfile inside the datastore.
Proactive Measures in Virtualization Infrastructures
Before datastore access problems occur, the infrastructure must be designed in a redundant and traceable manner.
- Multipathing Configuration: There must always be at least two active physical paths between ESXi hosts and storage. Native Multipathing (NMP) or vendor-specific multipathing software (e.g., Dell PowerPath) must be enabled to ensure that traffic continues uninterrupted in the event of a single cable or switch failure.
- Proactive Monitoring: Continuous analysis of logs and performance metrics allows you to detect potential outages in advance. To monitor your network activity and catch threats instantly, you can benefit from our SOC-Focused Security Incident Monitoring and Response service.
For similar storage problems and solutions you may encounter in the virtualization layer, you can review our VMware Cannot See Datastore Issue guide. Additionally, to set up a secure storage space from scratch, you can check out our VMware iSCSI Datastore Installation article.
To receive expert support in the design, installation, performance optimization, and troubleshooting of your enterprise virtualization infrastructure, you can review our Managed Virtualization Infrastructure Service solutions or contact us directly.
Frequently Asked Questions
Is virtual machine data deleted when the Datastore is in Inaccessible status?
No, the datastore being inaccessible does not mean the data is deleted. Only the communication between the ESXi host and the storage is disconnected. When the connection is re-established, your data will be accessible from where it left off. However, there may be a risk of corruption in data being written to disk at the time of the outage.
How do I tell the difference between APD and PDL?
In an APD (All Paths Down) state, the ESXi host assumes the device will return and tries to keep the paths open, producing an "all paths down" warning in the logs. In a PDL (Permanent Device Loss) state, the storage unit explicitly informs the ESXi host that the device is no longer there, and "Permanent Device Loss" or "SCSI sense codes" are seen in the logs.
Does the Storage Rescan process cause downtime in the production environment?
No. The Storage Rescan process you will perform on the ESXi host is completely harmless and does not cause any downtime or performance loss on your running virtual machines. On the contrary, it is a routine process for detecting newly presented disks or recovered connections.
Conclusion
The VMware Datastore Inaccessible error is one of the most critical emergency scenarios for virtualization administrators. With correct multipathing configuration, regular physical checks, and log analysis, a large portion of these problems can be permanently prevented or resolved in a very short time. For the continuity and security of your virtualization environment, our proactive management services are always by your side.
