Microsoft SQL Server Virtual Backup Device Specification
VDConfig Structure
This table lists the client inputs to the VDConfig structure.
| Field | Type | Value |
|---|---|---|
| deviceCount | UINT32 | This is the number of devices, from 1 to 64, to be used. |
| features | UINT32 | This is a bit mask of features. For more information, see Feature Bits. |
| prefixZoneSize | UINT32 | This is the size, in bytes, of the prefix zone. The value 0 indicates that no prefix zone will be used. The zone appears at a negative offset from the aligned data buffers. |
| alignment | UINT32 | This is the minimum alignment of buffers required by the client. For example, 1024 indicates that any buffer must have the data zone starting at a 1-KB boundary. |
| softFileMarkBlockSize | UINT32 | This field is used only when VDF_FileMarks is set. If the field is set to zero, then the Microsoft Tape Format (MTF) control blocks indicate that softFileMarks are not used. For any other value, this field provides the size, in bytes, of the softFileMarks implemented by the client. The server uses this value to format the MTF control blocks properly.
SQL Server writes this value into the MTF control block fields that require the softFileMarkBlockSize. |
| EOMWarningSize | UINT32 | This is the size, in bytes, of the end of the media warning zone. If this field is set to 0, SQL Server will not attempt to constrain itself for this factor.
For more information, see End Of Media and Unexpected Filemarks. |
| serverTimeOut | UINT32 | This is the time-out, in milliseconds, used by SQL Server to limit the client response time.
The value 0 causes an infinite time-out. |
This table lists the server inputs to the VDConfig structure.
| Field | Type | Value |
|---|---|---|
| blockSize | UINT32 | This is the size, in bytes, that is used as the device BLOCKSIZE. |
| maxIODepth | UINT32 | This field is deprecated. It is now always returned as 4. This used to be the count of the maximum number of I/O requests outstanding at any one time. |
| maxTransferSize | UINT32 | This is the size, in bytes, of the maximum I/O request that is issued by SQL Server to the device. This is the size of the data portion of the buffer. |
| bufferAreaSize | UINT32 | This field is deprecated. It is now always returned as maxTransferSize * 4 * deviceCount. This used to be the byte count of the total amount of space being used for buffer memory. |