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Disabling Hardware Accelerated Init (WRITESAME) in ESXi (2146566)

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ESXi hardware acceleration supports these array operations: 
  • Atomic Test & Set (ATS), which is used during creation and locking of files on the VMFS volume
  • Clone Blocks/Full Copy/XCOPY, which is used to copy or migrate data within the same physical array
  • Zero Blocks/Write Same, which is used to zero-out disk regions
Block zeroing, also called write same. Enables storage arrays to zero out a large number of blocks to provide newly allocated storage, free of previously written data. This operation reduces the time and network load when creating virtual machines and formatting virtual disks.
The fundamental operations are controlled by these advanced settings: 
  • HardwareAcceleratedLocking
  • HardwareAcceleratedMove
  • HardwareAcceleratedInit
 This article explains how to disable HardwareAcceleratedInit (WRITESAME) in ESXi.


To disable hardware accelerated init a.k.a. WRITESAME or vendor specific SCSI command 0xFE use this ESXCLI command:

esxcli system settings advanced set --int-value 0 --option /DataMover/HardwareAcceleratedInit


Note: This option is effective immediately and does not need any reboot or mount/unmount of volumes.

To disable HardwareAcceleratedInit using the vSphere Web Client, follow the below procedure:
  1. Browse to the host in the vSphere Web Client navigator.
  2. Click the Configure tab.
  3. Under System, click Advanced System Settings.
  4. Change the value for DataMover.HardwareAcceleratedInit to 0 (disabled).

Note: This option is effective immediately and does not need any reboot or mount/unmount of volumes.

Additional Information

This is a list of commonly used SCSI opcodes related to VAAI operations:

0x93 WRITE SAME(16)
0x41  WRITE SAME(10)
0x42  UNMAP

Occasionally, failures during VAAI operations would be logged in the /var/log/vmkernel.log file. For example:

Cmd(0x41248092e240) 0x42, CmdSN 0x13bb23 to dev "naa.xxxxxxxx" failed H:0x0 D:0x2

See Also

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