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Pool or Device Configuration Prevents Storage Device Removal (KBA4378)



KBA# 4378

Troubleshooting Storage Device Removal 

Attempting to remove a device from the Delphix engine's storage pool results in the following error:

The pool or device configuration prevents removal.

This can be caused by a mismatch in the sector sizes of the disks within the storage pool.

Disk devices are formatted with a physical sector size of either 512 bytes (known as '512 native' or 512n) or 4K.  To allow for backwards compatibility, some storage devices that use a physical sector size of 4KB can also emulate a 512 byte sector size, known as '512 byte emulation' or 512e.  However, these devices may still be seen by the Delphix engine as having a sector size of 4KB despite having a logical sector size of 512 bytes.

This table shows the relationship between the physical and logical sector sizes for each disk format.

Disk Format Physical Sector Size (bytes) Logical Sector Size (bytes)
512n 512 512
512e 4096 512
4K 4096 4096

Delphix device removal is only permitted if the physical sector sizes match for all disk devices within the storage pool.

The sector size of disks presented by VMware to guest VMs differ according to the type of virtual disk created.

Raw Device Mapping (RDM) devices, whether in virtual or physical compatibility mode, expose the sector sizes of the underlying disk device.  For a 4K disk operating in 512e mode, the Delphix engine will see a logical sector size of 512 bytes but a physical sector size of 4KB.

Virtual Machine Disk (VMDK) devices always use a 512 byte sector size.  This is documented by VMware here - Versions of VMFS Datastores - where the 'Virtual disk emulation type' is listed as 512n.  When using VMDKs, the Delphix engine will therefore see a physical sector size of 512 bytes.


Please contact Delphix Support to investigate how the affected disk can be removed from the storage pool.