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NDMP – Frequently Asked Questions

1. What is NDMP?
2. What NDMP resources currently exist?
3. What is the latest revision of the NDMP specification?
4. What good is the NDMP SDK?
5. What NDMP products currently exist?
6. What tape format does NDMP use?
7. How does NDMP control a tape drive?
8. How does NDMP control a tape library?
9. What is meant by 3-way backup?
10. Can I use NDMP to do a network copy?


1. Q: What is NDMP?

NDMP is an acronym for Network Data Management Protocol and is an open standard protocol for enterprise-wide backup of heterogeneous network-attached storage. NDMP was co-invented by Network Appliance and PDC Software (acquired by Legato Systems, Inc., and now part of EMC.).

The Network Data Management Protocol is defined in fine granularity within the NDMP specification. However, a quick synopsis follows:

Currently an NDMP server can be thought of providing two services:

  1. A DATA server - This service either reads from disk and produces an NDMP data stream (in a specified format) or reads an NDMP data stream and writes to disk, depending upon whether a backup or restore is taking place.


  2. A TAPE server - This service either reads an NDMP data stream and writes it to tape or reads from tape and writes an NDMP data stream, depending upon whether a backup or restore is taking place. All tape-handling functions, such as split-image issues, are dealt with by this service.
Each service has a separate state diagram that dictates its behavior, e.g. the tape server (mover state machine) can enter the pause state while tapes are being changed by the NDMP client.

NDMP messages are categorized into distinct groups or NDMP interfaces, such as SCSI, CONFIG and TAPE. These messages (as well as actions and errors) can trigger state changes.

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2. Q: What NDMP resources currently exist?

You can sign up for the NDMP email discussion groups. In addition, the following documentation and software can be downloaded from this website:

   NDMP specification document
   NDMP workflow analysis document
   NDMP rpcgen input (.x) file
   NDMP software development kit (SDK)
An ftp site (ftp.ndmp.org) also exists for downloading the above documentation and SDK as well as some contributed software.

In addition a Technical Working Group has recently been formed within the Storage Networking Industry Association (SNIA) to create a Software Developers Kit for NDMP version 4.0. See www.SNIA.org for more infomation.

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3. Q: What is the latest revision of the NDMP specification?

The latest NDMP revision is v4.

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4. Q: What good is the NDMP SDK?

The NDMP software developers kit is developed to prototype new NDMP functionality added and provides a functional (although fairly basic) implementation of an NDMP client and NDMP server.

The objective of the SDK is to facilitate rapid development of NDMP compliant clients and servers on a variety of platforms.

Third parties are welcome to download the NDMP v3 software developers kit and make use of the provided source code within your products (subject to copyright notices supplied) or as example/reference code.

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5. Q: What NDMP products currently exist?

The NDMP Product Directory contains a list of all shipping NDMP-compliant products.

A contributed software package called NDMPcopy is available and allows data from one NetApp filer to be copied to another NetApp filer using NDMP.

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6. Q: What tape format does NDMP use?

In theory NDMP doesn't care about tape formats. The NDMP DATA server produces an NDMP stream and this is simply written straight to tape by the NDMP TAPE server.

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7. Q: How does NDMP control a tape drive?

NDMP has a TAPE interface that allows an NDMP client to position tape and read/write tape labels, etc.

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8. Q: How does NDMP control a tape library?

NDMP has a SCSI interface that allows an NDMP client to pass SCSI CDBs (command data blocks) through to the SCSI tape library attached to the NDMP server.

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9. Q: What is meant by 3-way backup?

NDMP v1 only allowed backing up data to locally attached tape devices.

NDMP v2 makes it possible to direct the NDMP data stream from one NDMP server via a (fast) network connection to a remote NDMP server. The remote NDMP server can then access tape locally.

This is known as 3-way backup, since typically 3 hosts are involved:

  1. The host running the NDMP client.
  2. The host running the NDMP DATA server.
  3. The host running the NDMP TAPE server.
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10. Q: Can I use NDMP to do a network copy?

Only on NetApp filers, since a private extension was added so that this would be possible within NDMP v2. The contributed software, NDMPcopy, is an NDMP client that makes use of this extension.

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