Snapshot or backup fails because a virtual disk file is missing #

A missing virtual disk data file, such as a -flat.vmdk file referenced by a VMDK descriptor, can prevent VMware vSphere from creating a VM snapshot. This can also cause XVault backup operations that require a VM snapshot to fail.

If you encounter this issue, review the snapshot task error in vSphere and verify that the files referenced by the VM’s virtual disk configuration are present and accessible. If a required file is missing, contact your VMware support provider for recovery assistance. Do not delete or modify virtual disk files as a troubleshooting step.

If vSphere snapshots complete successfully but XVault backups continue to fail, contact QSAN Support and provide the backup error message and relevant logs.

VMware ESXi does not detect an iSCSI LUN #

If an iSCSI LUN from a QSAN storage system does not appear under Storage Devices on the VMware ESXi host, follow these steps:

1. Check iSCSI connectivity and discovery. Verify that the ESXi host can reach the iSCSI target and that the target IP address is correct in the adapter’s discovery settings. If CHAP is enabled, verify that the authentication settings match on the host and the storage system.
2. Check the LUN mapping. On the QSAN storage system, verify that the LUN is mapped to the intended ESXi host and that the host entry contains the correct iSCSI initiator IQN.
3. Verify the LUN’s logical block size. ESXi does not support iSCSI LUNs presented by an external storage array with a logical block size of 4,096 bytes (4Kn). Check the logical block size reported to ESXi. If the LUN is presented as 4Kn, contact QSAN Support to confirm the options available for your storage system.
4. Rescan the storage adapter. After correcting any configuration issues, rescan the iSCSI storage adapter and check whether the LUN appears under Storage Devices.

VMFS datastore is inaccessible in VMware ESXi #

If an ESXi host can’t access a VMFS datastore on a QSAN storage system, follow these steps:

1. Check storage connectivity. Verify that the LUN backing the datastore is visible to the affected ESXi host and that the expected storage paths are available. If the LUN is missing or its paths are unavailable, resolve the connectivity issue and rescan the storage adapters.
2. Check the mount status. If the LUN is visible but the datastore is unmounted, verify that it is the expected datastore, then mount it on the affected host. Check whether access is restored.
3. Review any remaining errors. If the datastore is still inaccessible, record the error shown in the vSphere Client. If the error indicates possible VMFS corruption, contact VMware Support for guidance before attempting any file system repair.

How to troubleshoot slow storage reads in VMware vSphere #

If a virtual machine experiences slower than expected read performance on QSAN storage, use the following steps to narrow down the cause:

1. Record the current configuration. Note the storage model, firmware version, ESXi version, and storage protocol. Record which VMs are affected and when the slowdown occurs.
2. Check the storage paths on the ESXi host. If multipathing is configured, verify that the expected paths are available and review the path selection policy. Use Round Robin with an IOPS limit of 1 only if QSAN recommends this setting for your storage model and ESXi configuration.
3. Review the settings relevant to the workload. Consult the QSAN Storage Performance Tuning Guide for recommendations that apply to your setup. If the slowdown occurs when a Windows VM reads data over the network, also check the VM’s network adapter settings. Retest with the same workload after each change.
4. Isolate the network path if needed. If the storage system supports a direct connection to the ESXi host, test it during a maintenance window to help determine whether the switch or network path contributes to the slowdown.