Networker

Re: [Networker] Restore questions

2005-06-23 13:53:58
Subject: Re: [Networker] Restore questions
From: "Werth, Dave" <dave.werth AT GARMIN DOT COM>
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Date: Thu, 23 Jun 2005 12:41:25 -0500
Scott,

I'm well aware of the possibility of previously deleted files being restored
when you run a saveset restore and specifically warned my users about that
when we finished the restore.

As far as the index scanning issue, when we started the non-saveset restore
of the E drive it took perhaps 5 minutes for Networker User to scan the
indexes and decide what files it was going to restore before it actually
started reading from tape and restoring files.  And yet it still took about
2.5 hours more to restore a drive (on the same RAID) that had about 2 GB
less space used and 128,620 fewer files (only 62.5% of the number on F).  So
it appears to me that there is more going on in a non-saveset restore, even
after the files actually start restoring.  I suppose it has to do with the
fact that during a saveset restore it doesn't have to decide if a particular
file it finds in the restore stream should be restored or not.

When your file server has been down for 2 days because the support techs
can't figure out how to get it fixed (don't get me started but to be fair it
turned out to be a pretty obscure problem that destroyed the RAID) and users
are getting desperate you want to get the restore done ASAP and worry about
the loose ends later.  Thankfully this is only the 3rd such incident of this
magnitude in the 20 years I've been here (the other 2 were before the days
of RAID).

Dave

David Werth
Garmin AT, Inc
Salem, Oregon
dave.werth AT garmin DOT com

-----Original Message-----
From: Scott Russell [mailto:lnxgeek AT us.ibm DOT com] 
Sent: Wednesday, June 22, 2005 9:22 PM
To: Legato NetWorker discussion; Werth, Dave
Subject: Re: [Networker] Restore questions

Werth, Dave wrote:
> The restore of E:\ took about 11 hours.  The restore of F:\ took about 8.5
> hours (including restoring the 2 incrementals that followed it).  Since
the
> two drives are of similar size (F being 3.6% larger) that is a substantial
> difference.

Right here is the potential trap with saveset recoveries. Suppose you 
have the following situation:

Day 1: Full back up drive E:\
Later that day after the full backup:
   .. Existing FileA deleted
   .. New FileB added
   .. Existing FileC modified
Day 2: Incremental backup of drive E:\

Now let's say on Day 3 you have to restore the entire drive E:\. When 
you restore the saveset from Day 1 you're going to get FileA, FileB, and 
FileC. When you restore the saveset from Day 2 you're going to get the 
updated version of FileC.

What you're left with is FileA which shouldn't be there after Day 2 
anyway. In other words, when restoring using multiple savesets depending 
on your backup strategy it is possible to end up with extra files that 
were deleted.

As far as index scanning goes, savesets are faster because the up front 
time to calculate what files need restoring isn't done however with an 
index based recovery you eliminate the problems of extra files showing 
up. As far as I've seen the index scanning only takes place PRIOR to the 
file copies off the tape to the disk. Once the files start moving off 
the tapes the index based recovery doesn't appear any slower or faster 
than a saveset recovery.

All based on observation and experience. I should really read the 
manuals some day. ;)

-- 
Scott Russell <lnxgeek AT us.ibm DOT com>
IBM Linux Technology Center System Admin


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