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iservervirtualdeviceset2-requestbuffers.md

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title IServerVirtualDeviceSet2::RequestBuffers
titlesuffix SQL Server VDI reference
description This article provides reference for the IServerVirtualDeviceSet2::RequestBuffers command.
ms.date 08/30/2019
ms.prod sql
ms.prod_service backup-restore
ms.technology backup-restore
ms.topic reference
author mashamsft
ms.author mathoma

IServerVirtualDeviceSet2::RequestBuffers (VDI)

[!INCLUDEappliesto-ss-xxxx-xxxx-xxx-md]

The RequestBuffers function informs the VDI that the server will need a certain number of buffers with a given size and alignment requirement.

Syntax

HRESULT IServerVirtualDeviceSet2::RequestBuffers (
   DWORD   dwSize,
   DWORD   dwAlignment,
   DWORD   dwCount
);

Parameters

dwSize Identifies the size of each buffer. This size should only include the region needed for data. The VDI takes care of any alignment and prefix requirements.

dwAlignment The alignment required for these buffers. A value more restrictive than the basic alignment value specified with 'BeginConfiguration' may be used. If the value is 0, it will default to the basic alignment value.

dwCount The number of buffers which will be requested by 'AllocateBuffer' with the given size and alignment.

Return Value

Return Value Explanation
NOERROR The function succeeded.
VD_E_ABORT Abort was requested.
VD_E_PROTOCOL The set is not in a state in which buffer allocations may be declared (see the state transition matrix).
VD_E_MEMORY The requested memory could not be obtained.

Remarks

This method should be used before buffers are allocated with AllocateBuffer. Sets of buffers with a given size and alignment are requested with RequestBuffers and then individual buffers are allocated with AllocateBuffer.

During the configuration phase, RequestBuffers calls are "summed" together so that at the EndConfiguration call a single buffer area can be used (it is allocated at that time). After configuration is complete, any RequestBuffers calls result in immediate allocation of more buffer space.

Next steps

For more information, see the SQL Server virtual device interface reference overview.