From the way I read the spec for NDMP it defines a method for writing
data to tape, not just moving data from tthe NAS too a backup
application. Do backup vendors actually write NDMP daata streams
directly to tape, or do they typically encapsulate in their own
proprietary on tape format?
--
Nik Simpson

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On Tue, 10 Jul 2007 17:33:48 -0400, Nik Simpson
<n_simpson@bellsouth.net> wrote:

> From the way I read the spec for NDMP it defines a method for writing
>data to tape, not just moving data from tthe NAS too a backup
>application. Do backup vendors actually write NDMP daata streams
>directly to tape, or do they typically encapsulate in their own
>proprietary on tape format?

I have not heard of NDMP specifying a format, but I've never actually
read the spec.

In the case of NetApp, it uses dump/restore format; basic Unix
commands.  It uses the same format when moving data between filers,
not just to tape.  So an NDMPcopy between filers uses dump|restore.

EMC uses a proprietary backup format but that's case regardless of
NDMP being in the picture.  It's just the format it uses.

I can't say anything about other vendors but I recall someone posting
about getting NDMP to work for Linux clients, which would likely use
native formats.

Veritas uses gnutar to write to tape, not sure about others.

I am skeptical about NDMP actually defining the format, from
everything I've ever heard and seen it's simply a command protocol,
not even a transport.

~F

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Faeandar wrote:
>
>
> I am skeptical about NDMP actually defining the format, from
> everything I've ever heard and seen it's simply a command protocol,
> not even a transport.
>

Thanks, I was a little surprised myself which is why I asked, the
question arose after reading the NDMP FAQ on ndmp.org which says:

The NDMP 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.


But on reflection, (2) could simply refer to any backup server that can
handle the NDMP stream, in which case the description is somewhat
ambiguous as to whether the NDMP stream is written to tape directly, or
the TAPE server has to interpret and rewrite it in whatever tape format
it uses.

--
Nik Simpson

[ Post a follow-up to this message ]

On Tue, 10 Jul 2007 19:24:06 -0400, Nik Simpson
<n_simpson@bellsouth.net> wrote:

>Faeandar wrote: 
>
>Thanks, I was a little surprised myself which is why I asked, the
>question arose after reading the NDMP FAQ on ndmp.org which says:
>
>The NDMP 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.
>
>
>But on reflection, (2) could simply refer to any backup server that can
>handle the NDMP stream, in which case the description is somewhat
>ambiguous as to whether the NDMP stream is written to tape directly, or
>the TAPE server has to interpret and rewrite it in whatever tape format
>it uses.

I'm guessing you are hung up on the "produces an NDMP data stream (in
a specified format) "?
The specified format is determined by the source/destination, not by
NDMP.  NDMP simply carries out the commands for the format.

Given that NDMP is not a format, (2) would be specific to the native
format of the backup server (like gnutar in the case of Veritas). The
NDMP stream is ripped apart if it goes to a media server, or it's
nothing more than a command protocol on the case of direct-to-tape.
Again I use NetApp as an example.  If I use Veritas to tell a filer to
backup to tape, it is done over NDMP.  But the filer actually sends
dump format to tape.  NDMP is only ever used to accept commands -from-
the backup server and send information -to- the backups server
(catalogue, end of tape, etc.)

~F

[ Post a follow-up to this message ]

Faeandar wrote:

>
> Given that NDMP is not a format, (2) would be specific to the native
> format of the backup server (like gnutar in the case of Veritas). The
> NDMP stream is ripped apart if it goes to a media server, or it's
> nothing more than a command protocol on the case of direct-to-tape.
> Again I use NetApp as an example.  If I use Veritas to tell a filer to
> backup to tape, it is done over NDMP.  But the filer actually sends
> dump format to tape.  NDMP is only ever used to accept commands -from-
> the backup server and send information -to- the backups server
> (catalogue, end of tape, etc.)
>


Thanks for the clarification.

--
Nik Simpson

[ Post a follow-up to this message ]

The format used by NDMP is NOT in the Spec.  It's the only way they got
all the NAS vendors to agree to use it.  NDMP is only a communication
protocol.  It says "hi.  I'm here to back you up, please send a backup
stream to this device."  NDMP then does what it's told and tells your
backup app what it sent and where it sent it.

Think of it like a database app.  RMAN is a control protocol, not a
format.  Your backup app says "hi. I'm here to backup your Oracle
database.  Please send a backup stream to there."  RMAN then does what
it's told and tells your backup app what it sent and where it sent it.

In neither case does your backup app understand the format of what has
been sent to tape.  It does not translate it into it's own format, but
it MAY put some blocks at the beginning and end so that it understands
that it's an NDMP/RMAN image, but it does not translate/encapsulate the
stream itself.  In the case of NDMP, it's going to be dump/tar/cpio, or
whatever the filer vendor chose.

Because of that, you CANNOT restore a NetApp NDMP backup to a
Bluearc/Onstor, etc.  If you happen to have a Unix box, you can use the
manual and mt to position the tape to the point where the dump starts,
then use dump to read the backup, but you'll lose any Windows ACLs you
had stored in there, as NetApp hacked dump to support ACLs (and all the
other NAS vendors did the same thing).

This is why I recommend NDMP ONLY for backups -- not archives.  If
you're going to archive data, it needs to be in a platform-independent
format, and NDMP is not platform-independent.  I recommend NDMP only for
backups.

If your backup software supports synthetic full backups, you can read a
blog entry I wrote about an alternative to NDMP:

http://www.backupcentral.com/content/view/48/47/


I hope this helped.

---
W. Curtis Preston
Backup Blog @ www.backupcentral.com
VP Data Protection, GlassHouse Technologies=20

-----Original Message-----
From: comp.arch.storage-bounces@backupcentral.com
[mailto:comp.arch.storage-bounces@backupcentral.com] On Behalf Of Nik
Simpson
Sent: Tuesday, July 10, 2007 2:34 PM
To: comp.arch.storage@backupcentral.com
Subject: [C.A.S.] NDMP Question

From the way I read the spec for NDMP it defines a method for writing=20
data to tape, not just moving data from tthe NAS too a backup=20
application. Do backup vendors actually write NDMP daata streams=20
directly to tape, or do they typically encapsulate in their own=20
proprietary on tape format?
--=20
Nik Simpson
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