[Novalug] need dd help

John Franklin franklin@elfie.org
Mon Feb 13 08:58:20 EST 2012


Can you open another shell and run vmstat?  How fast is it writing?

jf

On Feb 13, 2012, at 5:49 AM, Jay Hart wrote:

> After 8 hours, I'm still waiting for the dd command to complete.
> 
> Jay
> 
>> Sounds a bit short.  100MB/s write speed would take 10,000 seconds to zero a
>> 1TB drive.
>> 
>> jf
>> 
>> On Feb 13, 2012, at 12:36 AM, Jay Hart wrote:
>> 
>>> Not sure I understand what you are saying.  I should take a value such as 8
>>> seconds and multiply by a 1000?
>>> 
>>> So 8000 seconds should be over 2 hours and 10 minutes.  Sound about right to
>>> zero a 1TB drive?
>>> 
>>> Jay
>>> 
>>>> On Sun, Feb 12, 2012 at 10:37:22PM -0500, Jay Hart wrote:
>>>>> Jon,
>>>>> 
>>>>> So this will wipe my entire drive, 1k at a time.  1TB will take a while, I
>>>>> suspect.
>>>> 
>>>> Preview it by doing
>>>> 
>>>> time dd if=/dev/zero of=junk bs=1k count=1048576
>>>> 
>>>> and multiple the time by 1000.  That should give an outer limit.
>>>> 
>>>> You could also try
>>>> 
>>>> time dd if=/dev/zero of=junk bs=4k count=262144
>>>> 
>>>> and see if there is a speed-up.
>>>> 
>>>> Running the 1k command on three different systems I got 29,
>>>> 11, and 3 seconds.  Guess which one had the Solid State Drive :)
>>>> The 4k command ran about 20% faster.
>>>> 
>>>> Jon
>>>>> 
>>>>>> On Sun, Feb 12, 2012 at 10:17:04PM -0500, Jay Hart wrote:
>>>>>>> I think this command with totally wipe a drive:
>>>>>>> 
>>>>>>> dd if=/dev/zero of=/dev/devicename bs=1k
>>>>>>> 
>>>>>>> Yes/no. what exactly does the "bs=1k" do???
>>>>>> 
>>>>>> By default dd uses input and output buffers of 512 bytes.
>>>>>> These can be changed individually with ibs= and obs=.
>>>>>> Your option bs= changes both buffer sizes to 1024 bytes.
>>>>>> 
>>>>>> I find when making large transfers like this that a
>>>>>> larger buffer size greatly speeds up dd.  I'd suggest 4k.
>>>>>> 
>>>>>> jl
>>>>>> --
>>>>>> Jon H. LaBadie                  novalugml@jgcomp.com
>>>>>> 11226 South Shore Rd		(703) 787-0688 (H)
>>>>>> Reston, VA  20190		(609) 477-8330 (C)
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>>>>> 
>>>>> 
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>>>> 
>>>> --
>>>> Jon H. LaBadie                  novalugml@jgcomp.com
>>>> 11226 South Shore Rd		(703) 787-0688 (H)
>>>> Reston, VA  20190		(609) 477-8330 (C)
>>>> _______________________________________________
>>>> Novalug mailing list
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>>> 
>>> 
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>> 
>> --
>> John Franklin
>> franklin@elfie.org
>> ICBM: 39º 01' 58.4"N 77º 24' 49.6"W Z+84m
>> 
>> 
> 

-- 
John Franklin
franklin@elfie.org
ICBM: 39º 01' 58.4"N 77º 24' 49.6"W Z+84m

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