Microsoft KB Archive/104223
PSS ID Number: 104223
Article Last Modified on 10/29/2003
The information in this article applies to:
- Microsoft Windows NT Server 3.1
- Microsoft Windows NT Workstation 3.1
This article was previously published under Q104223
The Windows NT Backup program uses Microsoft Tape Format (MTF) as its native format. In MTF, a collection of files backed up from a hard drive are stored on tape as a Data Set, and there may be multiple Data Sets per Tape. Data Sets may span one or more tapes. The term Tape Family refers to a collection of one or more Data Sets appended together and spanning one or more tapes. In Microsoft Tape Format (MTF) there are three major components:
- A Tape Data Block (Tape DBLK), otherwise known as the tape header
- One or more Data Sets
- On Tape Catalog Information (On Tape Catalog Inf)
|--------------------------------TAPE--------------------------------| |-----------------------DATA SET--------| |Tape | SSET | VOLB | DIRB | File | E Set | On Tape | E Set | |DBLK | DBLK | DBLK | DBLK | DBLK | DBLK | Catalog Inf| DBLK2 |
Tape Data Block
Every MTF tape contains one, and only one, Tape Descriptor Block. The Tape Descriptor Block must be the first object on the tape. The Tape Descriptor Block's primary purpose is to identify the tape. In order to accomplish this it contains the following:
- Unique tape Family ID
- Tape sequence number to tell which tape it is in a family
- Date added to family
- Tape name and description
A Data Set includes Volume Descriptor Blocks that describe the logical source device where the files are located. The term volume refers to the logical device being backed up (such as the C: drive or server/volume on a network drive). The volume descriptor block is followed by one or more Directory Descriptor Blocks, which describes the directories being backed up from the logical device. File and accompanying Data Descriptor Blocks follow.
Each backup session is written to tape as a distinct data set. Tapes can contain multiple data sets, and a single data set can extend across multiple tapes. The MTF specification breaks down the data set into specific Data Blocks:
S Set Descriptor Block The Start of Data Set Descriptor block is a control structure that provides information about the current Data Set. This includes:
- A Data sequence number
- Data set password
- Encryption and compression algorithms used
- Date the backup was performed
Volb Descriptor Block The Volume Descriptor block is a control structure that provides information about the physical computer(s) on which the directories and files reside. This includes:
- Device Name (such as C:, D:, and so on)
- Volume Name (such as ENGSYS)
- Machine Name (for example, Clonex 386)
- Date the backup was performed
Dirb Descriptor Block The Directory Descriptor block is a control structure that provides information about the location of the files on the host computer. This includes:
- Directory attributes (such as ReadOnly)
- Directory name (for example, \test)
- Dates of modification, creation, backup and access
- Other tape related items
This is a required Descriptor block and there must be at least one DIRB Data Block in a data set. The DIRB Descriptor Block may have data associated with it to specify items such as extended attributes and Access Control List information. File Descriptor Block Contains items that relate to the file, which include:
- Basic file attributes (such as read-only)
- File name
- Dates created, modified, backed up, and accessed
- File size
This is a required Descriptor Block and there must be one File Descriptor Block per file.
There may be additional data associated with the File Descriptor Block that specifies items such as extended attributes and Access Control List information. Any file data for the specified file will follow this Descriptor Block. E Set (End of Data Set) Descriptor Block The End of Data Set #1 Descriptor Block is a control structure that provides an indication that the end of the Data Set has been reached.
In the event that there is On Tape Catalog Information in the same partition as the file data there will be a second End of Data Set following the On Tape Catalog Information. Otherwise, there will only be one End of Data Set Descriptor Block. This includes:
- Location of On Tape Catalog Information, if any
- Data Set sequence number
- Number of corrupt files found during backup, if any
This is a required Descriptor Block and must be located at the end of the set. In the implementation of the MTF on tape catalogs, a second E SET Descriptor Block will follow the on tape catalog information E Set (End of Data Set) Descriptor Block #2
The End of Data Set #2 is a control structure that provides an indication that the end of the current Data Set has been reached. This is only present if On Tape Catalog information is located in the same partition as the Data Set Information. The purpose of the send End of Set Data Block is to provide fast access to the On Tape Catalog Information. This includes the same information contained in the first E SET Descriptor Block.
On Tape Catalog Information
The On Tape Catalog Information provides a quick method of locating Data Sets and specific Files and Directories on the tape. This includes:
- File/Directory Detail information.
This provides specific location information about the Directories and Files in the preceding Data Set. If File/Directory detail is present, then a Set Map must also be provided.
- Set Map information.
This provides information about all the Data Sets on the Media. It includes the location of the File/Directory Detail for each Data Set. The Set Map may exist without File/Directory Detail being present.
File/Directory Detail and Set Map objects may be located in different areas of the tape. If the device supports multiple partitions, some or all of the On Tape Catalog objects may be located on this optional partition.
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