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Date: Mon, 3 Feb 2014 08:44:05 +0100
From: Matthias Apitz <guru@unixarea.de>
To: freebsd-questions@freebsd.org
Subject: dump(8) && -b option
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Hello,

Last weekend I was playing around with the dump options to improve the
dump speed to my external USB drive. I tried using the -b option to
increase the blocksize of the written junks:

# dump -0auL -b 100 -f - /usr 
...
  DUMP: finished in 40 seconds, throughput 7485 KBytes/sec

# dump -0auL -b 10 -f - /usr
...
  DUMP: finished in 70 seconds, throughput 4274 KBytes/sec

with -b 1000 the dump hangs forever:

# dump -0auL -b 1000 -f - /usr
...
  DUMP: dumping (Pass III) [directories]
(hangs)

on of its child is doing this where fd 3 is the device to be backed up:

pread(0x3,0x28809000,0x1000,0x89909000,0xa5,0xbfbfcc88) ERR#5 'Input/output error'
pread(0x3,0x28809000,0x1000,0x89909000,0xa5,0xbfbfcc88) ERR#5 'Input/output error'
pread(0x3,0x28809000,0x1000,0x89909000,0xa5,0xbfbfcc88) ERR#5 'Input/output error'
pread(0x3,0x28809000,0x1000,0x89909000,0xa5,0xbfbfcc88) ERR#5 'Input/output error'
pread(0x3,0x28809000,0x1000,0x89909000,0xa5,0xbfbfcc88) ERR#5 'Input/output error'

Why is this?

Maybe the best is doing the write to the disk with dd(1), for example
with

# dump -0auL -f - /usr  | dd bs=8m > /dev/da0s1a/usr.dmp

Any comments?  Thanks

	matthias


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