Microsoft KB Archive/250468

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Knowledge Base

How Removable Storage Manager and Programs Recognize Media

Article ID: 250468

Article Last Modified on 2/28/2007


  • Microsoft Windows 2000 Server
  • Microsoft Windows 2000 Advanced Server
  • Microsoft Windows 2000 Professional Edition
  • Microsoft Windows 2000 Datacenter Server

This article was previously published under Q250468


This article will describe in detail how Removable Storage Manager (RSM) and programs recognize tapes based on tape labels.


When you place media in a library or drive, RSM must read the media to determine what to do with it. There are several pieces of information on the media used to identify it:

Media Label Type - Application label. Often this is the name of the application that wrote the label.
Media-ID - A unique value that identifies this particular piece of media.
Label-Info - A friendly name for the media.

RSM refers to the label type and media-ID together as an OMID. Together they uniquely identify each tape.

NOTE: RSM does not record on-media identifiers for read-only or write-once media. Instead RSM uses volume and serial number information already associated with the media.

Each media label format requires a Media Label Library (MLL) used to identify media. An MLL is a dynamic link library (DLL) that can interpret the format of a media label written by an RSM aware application.

RSM includes three MLL files to interpret supported media labels (Mll_hp.dll, Mll_mtf.dll, and Mll_qic.dll). When RSM reads a media label, it communicates with each registered media label library to find out which application wrote the media label. Each label library looks at the data in the label and tries to recognize its format. If it is recognized, it extracts the Label Type, Media-ID and Label-Info information and returns it to RSM. A tape with a label format that no label library recognizes is placed in the Unrecognized pool. If a label library recognizes the format, but the OMID information is not already found in the database, then RSM places this tape in the Import pool. If RSM finds the OMID information in the database then RSM has seen this particular tape before, and returns it to the proper location.

Besides OMID's, RSM keeps additional information about media it knows about in a database and uses the database to mount media, track media usage, and media status based on the following database records.

LogicalMedia-ID (LMID) - Friendly logical name, description, and {GUID} recorded only in the RSM database.
PhysicalMedia-ID (PMID) - Friendly physical media name and {GUID} recorded only in the RSM database.
Partition-ID (PartID) - Friendly side name, description, and {GUID} recorded only in the RSM database.

You can change the physical media name, partition side name, and partition description name fields in the RSM GUI and have no effect on the OMID recorded on the physical tape media.

When you introduce new unused media to RSM, it contains no OMID and must be prepared by RSM before it can be used by a program. When RSM prepares a piece of media, it records a "free media" label on the media and moves it to the free media pool.

For example, the following scenario describes what happens when Windows 2000 Backup requests media.

Computer-A: You start Backup, select the files you want to back up, and then choose to write to "new media". Backup attempts to "allocate" a new tape, and RSM satisfies this request by finding an available tape in the free pool. RSM moves it to the Backup pool, creates an LMID and gives the LMID to Backup. Backup writes, using Microsoft Tape Format (MTF), a Media Label, Media-ID, and label-Info (friendly name) on the tape, and then passes the new OMID to RSM. RSM records it in its database and updates the PMID and PartID information for that piece of media. From then on Backup uses the LMID to refer to this tape. Backup completes the back up operation, and then dismounts the media to free up the device.

When you issue an eject command for that tape in computer-A, RSM ejects the tape and moves that tape to the "off-line media" library.

Computer-B: Now if you insert the tape into computer-B, RSM mounts the media and reads the OMID. RSM passes the media label to each MLL in turn to see if any recognize the tape so RSM can figure out what to do with the tape. Each MLL looks for two things: something which indicates what kind of label this is, and something that indicates exactly which tape this is. For tapes created using Backup, the Mll_mtf.dll recognizes the tape as an MTF tape and extracts its Media-ID. RSM takes this Media-ID and tries to find it in its database, but cannot because RSM on computer-B has never registered this tape before. RSM then creates a PMID and a PartID for the tape. This PMID and PartID have no relationship to the PMID and PartID that RSM on computer-A created. RSM puts this tape in the import pool. It stores the OMID with the PartID record. This OMID is exactly the same as the OMID stored for this tape on computer-A. When you open Backup, it looks in the import pool for MTF tapes. It finds this one, and then prompts you if you want to allocate it to Backup. If you click Yes, then Backup calls RSM to allocate it. RSM satisfies this request to allocate by moving the tape to the Backup pool, and then creates the LMID in the database. Next, RSM passes the LMID to Backup. From then on, Backup uses the LMID to refer to this tape. The LMID created on computer-B has nothing to do with the LMID stored on computer-A. When you append a backup set to the tape, the Media label, LMID, PMID, and PartID all stay the same.

If you append a backup set to the tape, and then eject the tape from computer-B, RSM ejects the tape and moves that tape to the "off-line media" library. Now we have two computers that know about this tape, and both have its location in the "off-line media" library.

Computer-A: When you insert the tape into computer-A again, RSM uses the MLLs to figure out what to do with the tape. RSM reads the OMID and asks each MLL in turn if it recognizes the tape. For this tape, the Mll_mtf.dll recognizes the MTF tape and its Media-ID. RSM receives the OMID and finds it in its database. RSM changes the location from the "off-line media" library to the library where it was inserted. Then you start Backup and click the Restore tab. Backup lists media using LMID Description information in the RSM database. If you have Backup catalog it, Backup has RSM "mount" the tape. Backup passes RSM the same LMID that RSM created when Backup first "allocated" the tape. RSM mounts the tape, and Backup finds the appended backup set, and you can restore data from computer-B.

If you overwrite the tape and change the label name, Backup writes a new OMID and informs RSM. RSM deletes the old OMID information for this tape, and then replaces it with a new RSM PartID record. For additional information about writing a new label, click the article number below to view the article in the Microsoft Knowledge Base:

234492 Backup Creates New Tape GUID When Writing New Label

This effects other computers that are still using the old OMID to identify the media shared between the computeres.

For additional information about RSM, click the article numbers below to view the articles in the Microsoft Knowledge Base:

240856 Removable Storage Manager Terms and Definitions

234420 Backup Cycles Between Cataloging and Mounting the Same Tape

Keywords: kbinfo KB250468