How do I determine the optimal blocking factor for tar?

How do I determine the optimal blocking factor for tar?

Post by Matt Auste » Tue, 19 Sep 1995 04:00:00

The subject line really says it all: I'm using tar for backups onto a
4mm SCSI drive.  The tar documentation says that a block size much
larger than the default of 20 will give higher throughput, but how
much larger?  Is there any way for me for me to figure out the optimal
block size, or at least to get a ballpark estimate, other than trial
and error?

Thanks in advance!
  Matt Austern                             He showed his lower teeth.  "We             mine is being wicked."


1. SCO tar error on block size (not block factor)

Someone recommended:
tar cvfb - ./config 32768 | compress | dd of=/dev/rmt/0m bs=32k  
tar: invalid blocksize. (Max 20)
0+1 records in
0+1 records out

Seeing his/her error i supposed that what they meant was the actual
size in bytes to match the 'dd' record size.  But
tar cvfB -  ./config 32768  | compress | dd of=/dev/rmt/0m bs=32k
tar: B: unknown option
Usage: tar -{txruc}[0-9vfbkelmnopwAFLTP] [tapefile] [blocksize]
[tapesize] files...
        Key     Device            Block   Size(K)    Tape
        0       /dev/rfd048ds9    18      360        No    
        1       /dev/rfd148ds9    18      360        No    
        2       /dev/rfd096ds15   10      1200       No    
        3       /dev/rfd196ds15   10      1200       No    
        4       /dev/rfd0135ds9   18      720        No    
        5       /dev/rfd1135ds9   18      720        No    
        6       /dev/rfd0135ds18  18      1440       No    
        7       /dev/rfd1135ds18  18      1440       No    
        8       /dev/rct0         20      0          Yes    
        9       /dev/rctmini      20      0          Yes    
        10      /dev/rdsk/fp03d   18      720        No    
        11      /dev/rdsk/fp03h   18      1440       No    
        12      /dev/rdsk/fp03v21 10      20330      No  

Is there a way to get tar to match the 'dd' record size please?

access to a news server; thanks!
Disclaimer: opinions expressed my own and not representative of my

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