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On Wednesday 30 Mar 2016 19:36:57 Meino.Cramer@×××.de wrote: |
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> Neil Bothwick <neil@××××××××××.uk> [16-03-30 17:12]: |
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> > On Wed, 30 Mar 2016 06:36:15 +0100, Mick wrote: |
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> > > Also worth mentioning is dcfldd which unlike dd can show progress of |
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> > > the bit stream and also produce hashes of the transferred output. It |
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> > > has the same performance as the dd command though. |
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> > |
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> > I can't find the reference right now, but I did read that dcfldd |
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> > determines the best block size on the fly if none is given. It's |
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> > certainly faster than dd when copying images to USB frives (my main use |
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> > for it) when given no block size. |
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This is good to know! I'll try to remember to use it more often. |
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> Sounds it will be the tool of choice for that purpose, Neil ! :) |
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> |
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> Best regards, |
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> Meino |
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dd defaults to bs=512, so it is going to be slow on transferring anything more |
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than a few megabytes. To find the optimum block size with dd you could run |
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something like this: |
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$ dd if=/dev/zero bs=512 count=2000000 of=~/1GB.file |
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2000000+0 records in |
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2000000+0 records out |
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1024000000 bytes (1.0 GB) copied, 13.8359 s, 74.0 MB/s |
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$ dd if=/dev/zero bs=1024 count=1000000 of=~/1GB.file |
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1000000+0 records in |
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1000000+0 records out |
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1024000000 bytes (1.0 GB) copied, 10.4439 s, 98.0 MB/s |
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$ dd if=/dev/zero bs=2048 count=500000 of=~/1GB.file |
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500000+0 records in |
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500000+0 records out |
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1024000000 bytes (1.0 GB) copied, 9.57416 s, 107 MB/s |
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$ dd if=/dev/zero bs=4096 count=250000 of=~/1GB.file |
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250000+0 records in |
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250000+0 records out |
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1024000000 bytes (1.0 GB) copied, 9.0178 s, 114 MB/s |
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|
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$ dd if=/dev/zero bs=8192 count=125000 of=~/1GB.file |
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125000+0 records in |
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125000+0 records out |
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1024000000 bytes (1.0 GB) copied, 9.47107 s, 108 MB/s |
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$ rm 1GB.file |
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On an old spinning disk of mine it seems that bs=4096 is a good size to select |
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for writing data to it. |
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NOTES: |
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====== |
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1. If you rm the 1GB.file in between tests you'll get a better number, but |
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I've been lazy and other than the first test with bs=512, the comparative |
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result between remaining tests remains consistent. |
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2. In the above test the dcfldd command gives similar transfer times with dd, |
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if you use the same block size. For larger files some difference may be |
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apparent. |
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3. In your case you can use the intended input/output devices, rather than |
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/dev/zero, in order to get representative read and write cumulative times. |
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-- |
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Regards, |
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Mick |
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