Date: Mon, 3 Feb 2014 06:13:10 -0700 (MST) From: Warren Block <wblock@wonkity.com> To: Matthias Apitz <guru@unixarea.de> Cc: freebsd-questions@freebsd.org Subject: Re: dump(8) && -b option Message-ID: <alpine.BSF.2.00.1402030557110.25123@wonkity.com> In-Reply-To: <20140203074405.GA10184@sh4-5.1blu.de> References: <20140203074405.GA10184@sh4-5.1blu.de>
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On Mon, 3 Feb 2014, Matthias Apitz wrote: > > 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? Don't know, but I remember searching and finding reports of problems with -b values larger than 64. Those reports are years old, and unfortunately I can't find them now. > 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 Could make for interesting benchmarks. My guess is that the benefits would taper off after a smaller buffer size than that. Using -b64 at the same time would probably help reduce overhead.
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