Disabling VAAI Thin Provisioning Block Space Reclamation (UNMAP) in ESXi 5.0

Products

VMware vSphere ESXi

Issue/Introduction

VMware introduced a new feature in vSphere 5.0 called Space Reclamation, as part of VAAI Block Thin Provisioning. Space reclamation is a garbage collection process that helps storage partners to efficiently reclaim deleted space in coordination with vSphere 5.0.

ESXi 5.0 issues UNMAP commands for Space Reclamation in critical regions during several operations with the expectation that the operation would complete quickly. Due to varied response times from the storage devices, UNMAP command can result in poor performance of the system and should be disabled on the ESXi 5.0 host.

This article shows how to disable the UNMAP command used for the Space Reclamation.

Symptoms:

Performing a Storage vMotion or a Virtual Machine Snapshot results in poor system performance.
A Storage vMotion or Virtual Machine Snapshot fails or times out.
In the /var/log/vmkernel.log file, you see entries similar to:

2011-12-07T08:55:04.792Z cpu40:8232)ScsiDeviceIO: 2305: Cmd(0x41248092e240) 0x42, CmdSN 0x13bb23 to dev "naa.60000970000292602427533030304536" failed H:0x0 D:0x2 P:0x0 Valid sense data: 0xb 0x44 0x0.
2011-12-07T08:55:04.932Z cpu40:8232)NMP: nmp_ThrottleLogForDevice:2318: Cmd 0x42 (0x41248092e240) to dev "naa.60000970000292602427533030304536" on path "vmhba2:C0:T0:L3" Failed: H:0x0 D:0x2 P:0x0 Valid sense data: 0xb 0x44 0x0.Act:NONE

Environment

VMware vSphere ESXi 5.0

Cause

VAAI Thin Provisioning is enabled by default on devices that adheres to T10 standards. ESXi identifies Thin Provisioned LUNs and issue UNMAP commands to reclaim deleted space on the storage. The implementation and response times for the UNMAP command may vary significantly among storage arrays.

This variation of response times in critical regions could potentially interfere with operations such as Storage vMotion and Virtual Machine Snapshot consolidation.

Resolution

This issue is resolved in ESXi 5.0 Patch 02. For more information, see VMware ESXi 5.0 Patch Image Profile ESXi-5.0.0-20111204001-standard (2009330).

To download the ESXi 5.0 Patch 02, see the VMware Download Center.

You can work around this issue on vSphere 5.0 hosts which have Thin Provisioned LUNs and T10 standard storage arrays.

Note: To verify that you have a T10 storage array, consult the VMware Compatibility Guide.

To avoid the use of UNMAP commands on Thin Provisioned LUNs:

Log in to your host using the Tech Support mode. For more information on using Tech Support mode, see Tech Support Mode in ESXi 4.1 and 5.0 (1017910).
From your ESXi 5.0 host, run this command:

esxcli system settings advanced set --int-value 0 --option /VMFS3/EnableBlockDelete
To verify this setting, run this command :

esxcli system settings advanced list --option /VMFS3/EnableBlockDelete

Path: /VMFS3/EnableBlockDelete

Type: integer

Int Value: 0 <<<<<<<<<< 0 means Disabled</b>

Default Int Value: 1

Min Value: 0

Max Value: 1

String Value:

Default String Value:

Valid Characters:

Description: Enable VMFS block delete

Notes:

This is a per-host setting and must be issued on each ESXi 5.0 host in your cluster. It works for both VMFS3 and VMFS5 datastores
ESXi 5.0 Update 1 and ESXi 5.1 includes an updated version of vmkfstools that includes the -y option to send the UNMAP command to the storage arrays regardless of the ESXi host’s global setting. For more information, see Using vmkfstools to reclaim VMFS deleted blocks on thin-provisioned LUNs (2014849)
In ESXi 5.5, vmkfstools -y is deprecated and has been replaced by the esxcli storage vmfs unmap command. However, issuing UNMAP is still disabled by default. Space reclamation can be done manually by running the esxcli storage vmfs unmap command. For more information, see Using esxcli in vSphere 5.5 to reclaim VMFS deleted blocks on thin-provisioned LUNs (2057513)

Additional Information

Using Tech Support Mode in ESXi 4.1, ESXi 5.x, and ESXi 6.x
Disabling the VAAI functionality in ESXi/ESX
VMware ESXi 5.0 Patch Image Profile ESXi-5.0.0-20111204001-standard
How to reclaim VMFS deleted blocks on thin-provisioned LUNs
Como desabilitar a recuperação de espaço em bloco do provisionamento dinâmico VAAI (UNMAP) no ESXi 5.0
Thin Provisioning Block Space Reclamation (VAAI UNMAP) does not work
Deshabilitar VAAI Thin Provisioning Block Space Reclamation (UNMAP) en ESXi 5.0
在 ESXi 5.0 中禁用 VAAI 精简置备块空间回收 (UNMAP)
ESXi 5.0 で VAAI シンプロビジョニングのブロック領域解放 (UNMAP) を無効化する

Impact/Risks:

Without disabling the UNMAP feature, you may experience timeouts with operations such as Storage vMotion migrations and Virtual Machine Snapshot Consolidation.