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:
Q234492 Backup Creates New Tape GUID When Writing New LabelThis effects other computers that are still using the old OMID to identify the media shared between the computeres.
Q240856 Removable Storage Manager Terms and Definitions
Q234420 Backup Cycles Between Cataloging and Mounting the Same Tape