I did some additional resarch on fragmentation.
According to the system admin guide for NetBackup DataCenter for Unix, page
643, "If an error occurs in a backup, the entire backup is discarded and the
backup restarts from the beginning, not from the fragment where the error
occurred."
It also appears from the reading that most people are right that
fragmentation was most likely designed more for disk media than for tape,
but it does explicitly state that, "Fragmenting tape backups can also speed
up restores because NetBackup can skip to the specific fragment before
starting its search for a file. Otherwise it starts at the beginning of the
tape and reads tar headers until it finds the desired file."
I would assume that fragmentation could help, but that you are not going to
see significant improvements until you have a large backup set to restore
from. I could also see this as being useful when restoring from a file
share server where you may have multiple thousands of files to restore in a
single backup image.
Like everything, the only proof is testing, which I have not had the
opportunity to do, as of yet.
Dan
-----Original Message-----
From: Rob Worman [mailto:rob AT worman DOT org]
Sent: Thursday, October 18, 2001 12:02 PM
To: Kratunis, Anthony; EBU (E-mail)
Subject: RE: [Veritas-bu] Fragment size settings
I think not. AFAIK the only checkpoint restart ability NetBackup can
provide is through the use of multiple streams backing up a single
backup class.
But if I'm wrong and you're right, Holy Hannah we should all be using
fragmentation! :-)
rob
--- "Kratunis, Anthony" <akratunis AT tiaa-cref DOT org> wrote:
> I seem to recall another benefit for fragments. If a backup segment
> fails,
> only that segment needs to be re-tried. So if a 10G file system is
> broken
> into 2G segments, and error is generated during the 9th G, only the
> last 2g
> are retried.
>
> Also, I thought the fragmentation was not used at all on backups to
> disk
> media servers, since a disk is not sequential but random access.
> anthony
>
> -----Original Message-----
> From: Jim Horalek [mailto:jhoralek AT veritas DOT com]
> Sent: Thursday, October 18, 2001 11:59 AM
> To: 'David A. Chapa'; Marelas, Peter; EBU (E-mail)
> Subject: RE: [Veritas-bu] Fragment size settings
>
>
> Disk storage Unit default "2000"
> Media Manager(tape) "0" unlimited.
>
> Tar does require you to be positioned at the start of the
> fragement for the restore. p643 Unix p490 Nt Sysadmin Guide 3.4.
> It actually says beginning of tape.
>
> So the default values are not necessarily the best.
>
> -Jim
>
> > -----Original Message-----
> > From: David A. Chapa [mailto:david AT xbpadm-commands DOT com]
> > Sent: Thursday, October 18, 2001 6:58 AM
> > To: Marelas, Peter; 'Jim Horalek'; EBU (E-mail)
> > Subject: RE: [Veritas-bu] Fragment size settings
> >
> >
> > Yes. That's the way it has been even back when I was with
> > OpenVision as one
> > of their consultants.
> >
> > What it does is lay down image fragment markers on the tape. when
> the
> > restore is performed, netBackup knows which image fragment
> > the file exists
> > in based on its database, so it can seek to the appropriate
> > image fragment,
> > then it begins reading the image fragment looking for the
> > file in question.
> >
> > As far as NBU doing seeking, it was my understanding that the
> > default was
> > 2048, does that mean EOT or unlimited? Or does that mean
> > 2GB? I know we
> > had that as a limit back when 2GB was a hard OS limit, but
> > what does it mean
> > now?
> >
> > Your point is a good one Peter.
> >
> > David
> >
> > <><><><><><><><><><><><><><><><><><><><>
> > David A. Chapa
> > NetBackup Consultant
> > DataStaff, Inc.
> > http://www.consulting.datastaff.com
> > 847 413 1144
> > ---------------------------------------
> > NBU-LSERV AT datastaff DOT com - Adv. Scripting
> > http://www.xbpadm-commands.com
> >
> > -----Original Message-----
> > From: veritas-bu-admin AT mailman.eng.auburn DOT edu
> > [mailto:veritas-bu-admin AT mailman.eng.auburn DOT edu]On Behalf Of
> Marelas,
> > Peter
> > Sent: Thursday, October 18, 2001 1:11 AM
> > To: 'Jim Horalek'; EBU (E-mail)
> > Subject: RE: [Veritas-bu] Fragment size settings
> >
> >
> > Are we sure about this?
> >
> > > The smaller the fragment size the faster the restore "might" be.
> > > Netbackup will make the tape drive "seek" to the correct fragment
> > > without reading the tape between.
> >
> > Are we saying Netbackup can not locate (seek) within a tar file?
> > If so, I would expect restoring a file at the end of a
> > DLT7000 tape (35GB)
> > reading at 5MB/s with 1 large 35GB fragment (1 tar file)
> > would take just
> > under two hour.
> >
> > This doesnt sound right to me especially considering the
> > default fragment
> > size is EOT.
> >
> > Regards
> > Peter Marelas
> >
> > -----Original Message-----
> > From: Jim Horalek [mailto:jhoralek AT veritas DOT com]
> > Sent: Thursday, 18 October 2001 2:49 PM
> > To: EBU (E-mail)
> > Subject: RE: [Veritas-bu] Fragment size settings
> >
> >
> > Well if you think about it, Netbackup streams data to the
> > storage device. If the storage device is a disk you can't
> > exceed the maxfile size for the partition. Tape has no
> > maxfile size. Netbackup will stream until EOT if you let it.
> > Luckly Netbackup will span tapes. Of course a Disk unit is
> > spanned via multiple files.
> >
> > The problem is the restore. If the largest file your extracting
> > from the fragment is larger than the maxfile size for the
> > partition it isn't going to fit. This doesn't happen very often.
> > Usually restoring to an altenate OS client.
> >
> > The Maxfile size is determined by the OS (solaris,sgi,NT) also
> > whether its 32bit or 64bit and the underlying filesystem.
> >
> > The smaller the fragment size the faster the restore "might" be.
> > Netbackup will make the tape drive "seek" to the correct fragment
> > without reading the tape between.
> >
> > Smaller fragments also means more wasted space on the tape.
> >
> > Jim
> >
> >
> > > -----Original Message-----
> > > From: Cornely, David [mailto:David_Cornely AT intuit DOT com]
> > > Sent: Wednesday, October 17, 2001 6:36 PM
> > > To: 'Zufall, Ken'; 'rob AT worman DOT org'
> > > Cc: EBU (E-mail)
> > > Subject: RE: [Veritas-bu] Fragment size settings
> > >
> > >
> > > What I can tell you about fragment size is this:
> > > The Veritas consultant that just audited our environment said
> > > the Fragment
> > > size for all storage units should be set to 2048.
> > >
> > > -----Original Message-----
> > > From: Zufall, Ken [mailto:Ken.Zufall AT ps.bellhowell DOT com]
> > > Sent: Wednesday, October 17, 2001 12:12 PM
> > > To: 'rob AT worman DOT org'; Zufall, Ken
> > > Cc: EBU (E-mail)
> > > Subject: RE: [Veritas-bu] Fragment size settings
> > >
> > >
> > > I've run into this problem before using Alexandria. Format
> > was cpio,
> > > fragment size was 2.5GB or thereabout on Solaris 2.5. When
> > trying to
> > > extract single files from the fragment I was unable to
> > > because of the size.
> > >
> > > Ken Zufall
> > > Work: 330.202.4113
> > > Cell: 330.465.8113
> > > Pager: 888.896.3272
> > > E-page: 4403037243.8963272 AT pagenet DOT net
> > > <mailto:4403037243.8963272 AT pagenet DOT net>
> > >
> > > -----Original Message-----
> > > From: Rob Worman [mailto:rworman AT yahoo DOT com]
> > > Sent: Wednesday, October 17, 2001 2:49 PM
> > > To: Zufall, Ken
> > > Cc: EBU (E-mail)
> > > Subject: Re: [Veritas-bu] Fragment size settings
> > >
> > > Are you saying that a Solaris version that
> > > doesn't support
> > > largefiles
> > > (ignoring the fact that that vintage of Solaris
> > > is no longer
> > > supported
> > > by NBU > 3.2...) would not be able to extract
> > > files from a
> > > tape that
> > > contains a 10 GB tar file? I can't disprove
> > > this fact, but
> > > I can doubt
> > > it. ;-)
> > >
> > > rob
> > >
> > > Zufall, Ken wrote:
> > >
> > > >Fragmentation shouldn't be a problem. Not
> > > sure about NBU,
> > > but other
> > > >applications I've worked with won't cut a file in the
> > > middle of a fragment,
> > > >it will continue to end of current file. So, if you've
> > > already backed up
>
=== message truncated ===
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