[Novalug] need dd help

Jason Kohles jkohles@palantir.com
Mon Feb 13 18:33:53 EST 2012


I think whoever said vmstat was thinking iostat..



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-----Original Message-----
From: Jay Hart [jhart@kevla.org<mailto:jhart@kevla.org>]
Sent: Monday, February 13, 2012 03:32 PM Pacific Standard Time
To: novalug@calypso.tux.org
Subject: Re: [Novalug] need dd help


Now I'm really confused, how does vmstat show the progress towards zeroing out
this drive?

Jay

> 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)
>>>>>>> _______________________________________________
>>>>>>> Novalug mailing list
>>>>>>> Novalug@calypso.tux.org
>>>>>>> http://calypso.tux.org/mailman/listinfo/novalug
>>>>>>>
>>>>>>
>>>>>>
>>>>>> _______________________________________________
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>>>>>>>> End of included message <<<
>>>>>
>>>>> --
>>>>> Jon H. LaBadie                  novalugml@jgcomp.com
>>>>> 11226 South Shore Rd              (703) 787-0688 (H)
>>>>> Reston, VA  20190         (609) 477-8330 (C)
>>>>> _______________________________________________
>>>>> Novalug mailing list
>>>>> Novalug@calypso.tux.org
>>>>> http://calypso.tux.org/mailman/listinfo/novalug
>>>>>
>>>>
>>>>
>>>> _______________________________________________
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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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