The main advantage is that it runs in parallel rather than in serial. For 
example, lets say your /vol/vol0 was 1TB, and had 10 qtrees each with 100MB in 
it. You could increase the client parallelism in legato to 10, and when you 
started the backup with a saveset of:
 
/vol/vol0/dir_a
/vol/vol0/dir_b
/vol/vol0/dir_c
/vol/vol0/dir_d
/vol/vol0/dir_e
/vol/vol0/dir_f
/vol/vol0/dir_g
/vol/vol0/dir_h
/vol/vol0/dir_i
/vol/vol0/dir_j
 
You would get 10 parallel backups each taking around 1/10 of what the volume 
backup would take. If you had the I/O and tape drive capacity, you would be 
reducing your backup time by 90%. Of course, that's an ideal situation.

________________________________

From: EMC NetWorker discussion on behalf of Kuin, CNM
Sent: Tue 2/26/2008 7:10 AM
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Subject: Re: [Networker] Long NDMP Backups



> You could backup the volumes on separate days, but since you
> are already doing a DSA backup (backing up via the net rather
> than direct backup), you are already getting the advantages
> of parallelization and variable block lengths. To increase
> the parallelization, you can change to backing up by qtree's
> rather than volumes. Each qtree will be parallelized with the
> backup. Also, the delay in the nsrdump is reduced since it
> has to walk a smaller part of the volume.
>
I was told NDMP isn't that efficient when defining qtree's vs volumes in
savesets.
It may limit the amount of data sent to the backupserver but it
increases the overhead on your filer because it has to determine, for
each saveset, which files to send over the wire. If you backup the
volume it has to do this once. If you backup per each individual qtree,
the filer has to do this X times.
Resulting in long wait times before data gets send over the wire.

I do think 12 hours to be quite fast btw. Our filer (3050, ONTAP 7.2.1)
does 2582GB, 8249432 files, in 16h 47m.

With regards,

Cor Kuin
Sysadmin
Waterlandziekenhuis

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