Re: [Veritas-bu] Multiplexing on VTL's

> I agree with b and c, but there a can be a little misleading 
> as we learned the hard way this past year.
> Netbackup records the start of a fragment and not the 
> location of the file on the tape. So it has to read the whole 
> fragment until it finds the file it is looking for.

Sounds as if you had a loooong restore experience, Len.  As mentioned, I
haven't empirically tested whether F-L-B is used in restoring part of a
multiplex set (if it's used in individual-file restore, you'd think it
would apply to finding the files of one backup in a mux set), but the
location of every file on the tape definitely is recorded--the block
numbers are field #5 in the output below:

# /usr/openv/netbackup/bin/cat_convert -dump *443_INCR.f
num     len     plen    dlen    blknum  ii      raw_sz  GB      dev_num 
  path 
  data
0       0       1       50      0       0       0       0       8388728 
  /    
  16877 root root 0     1209535204 1209430138 1209430138
1       0       5       49      1       1       0       0       8388731 
  /usr/ 
  16877 root sys  0     1209535162 1208501866 1208501866
[...]
18826   107     41      53      2286045 2       0       0       8388731 
  /usr/openv/netbackup/bin/private/nblogcfg       
  33088 root bin  54048 1208506181 1195233073 1209450948
18827   80      41      53      2286152 2       0       0       8388731 
  /usr/openv/netbackup/bin/private/nbloggen       
  33088 root bin  40024 1208506181 1195233073 1209450948
18828   73      41      53      2286232 2       0       0       8388731 
  /usr/openv/netbackup/bin/private/nblogmgr       
  33088 root bin  36564 1208506181 1195233074 1209450948
18829   111     42      53      2286305 2       0       0       8388731 
  /usr/openv/netbackup/bin/private/nblogview      
  33133 root bin  56304 1208506181 1195233074 1209450948


> -----Original Message-----
> From: veritas-bu-bounces AT mailman.eng.auburn DOT edu 
> [mailto:veritas-bu-> bounces AT mailman.eng.auburn DOT edu] On Behalf Of
bob944
> Sent: Wednesday, April 30, 2008 9:03 PM
> To: veritas-bu AT mailman.eng.auburn DOT edu
> Subject: Re: [Veritas-bu] Multiplexing on VTL's
> 
> 
> > My main concern is that when doing restores off a multiplexed
> > tape, the VTL READ speed off the disk(let's say it's 80MB/s)
> > is the same whether there's MPX in the stream or not. The
> > restore will throw away the bytes that doesn't belong to the
> > client, so out of a 80 MB/s stream coming off the disk, you
> > will throw away (let's say) 60MB and use only 20. It's this
> > reduction in effective restore speed that's my main concern.
> 
> Perhaps you'll have time to test and share here?  I'd expect NetBackup
> to treat it as multiplexed tape and not read the intervening 
> data.  IME,
> most multiplexed-tape-restore horror stories are no longer 
> valid due to
> a) fast-locate-block's ability to skip the intervening data (I have
> never explicitly tested this), b) drives that supply data faster than
> the client can write it and c) properly designed multiplexed 
> backups can
> restore multiple clients significantly faster than non-muxed (I have
> tested b and c).
> 


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