Most of what you say is correct, but Ontap 6.0 and greater supports DAR, due to NDMP allowing for cooperation between NDMP client and NDMP server.

When you run the backup, the filer sends "file history" information to the NDMP client. This information allows the NDMP client (Legato, Veritas, WorkStation Solutions, ArcServe, etc) to create the index of files in the backup _and_ their location in the backup stream (byte offset).

Meanwhile, the NDMP clients also track the amount of data written to each tape. So, when you do a DAR, the NDMP client tells the NDMP server (e.g. the filer) the list of files it wants restored and the offsets of those files. The filer and the NDMP client cooperate to load and position the tape to those offsets.

At each offset, the filer will extract the data and restore the requested file.

Which means: A) If you run an NDMP backup without file history (i.e. indexing) you can't run a direct access restore. B) To run a DAR, you need the functionality from the client and server. C) DAR is _possible_ using NDMP V2, V3, and V4 (all these versions support file history and the other commands necessary for DAR) D) Data Ontap 6.0 and greater supports DAR.

Hopefully this helps, Stephen Manley Member of the NDMP version of the Osmond family

On Thu, 4 Apr 2002, Surlow, Jim wrote:

Even though Networker might support DAR, does OnTap?

I did some research on this a while back (so my info may be dated), but my understanding is this:

The backup server initiates the NDMP command to the Filer (or other NDMP device), the OS on that device then begins to send data to tape by using means that it is aware of. In the case of OnTap, it uses the typical Unix dump command.

With dump/restore, there is no index created, thus, to recover, one has to scan from the beginning of tape of the first tape in the dump set until the data is found (on whatever tape). And the user waiting for the file will likely hope that their file is closer to the first part of the first tape rather than the last part of the last tape.

Netbackup & Networker will have an index knowing which NDMP tape set that a file is on, but I would guess that they would have no idea as to which tape in the set it is - or where on that tape (set: being number of tapes for that night's incremental, full, whatever).

If I'm off base, please clarify.

Thanks,

Jim Surlow CSG Systems

-----Original Message----- From: Alfred Lim [mailto:alfred@ptc.net] Sent: Thursday, April 04, 2002 10:23 AM To: toasters@mathworks.com Subject: Re: One more netbackup question...

Well one thing for Legato Networker, it support NDMP V3 and have this DAR feature.

-----Original Message----- From: "Jeff Kennedy" jlkennedy@amcc.com To: Don.Hickey@alcatel.com Date: Thu, 04 Apr 2002 08:56:46 -0800 Subject: Re: One more netbackup question...

...

Get a new backup software? The problem is that some vendors do not support Direct Access Restore, meaning it will search through every tape starting at the first and scan the whole thing. If no DAR, you're basically bummed.

Do you use snapshots? If you have the space it is a life-saver at times.

~JK

Don.Hickey@alcatel.com wrote:

...

I find restoring from a tape extraordinarly slowwwww. I have home directories on a clustered pair of F840 running 6.1.1r2. I have several volumes at about 300gb usable. When I need to restore a file from a users directory it can take up to 6+ hours (DLT 8000). It appears most of the time is taken searching for the files... is there anything you can suggest (including any white papers) to speed up this process?

thanks again

Don

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Jeff Kennedy Unix Administrator AMCC jlkennedy@amcc.com