Re: RAID 5 build time optimization question and experiments.

[Michael Evans <mjevans1983@gmail.com>]

On Fri, Dec 11, 2009 at 8:57 AM, Cat'Killer <catkiller@gmail.com> wrote:
>> On Fri Dec 11, 2009 at 02:55:31PM +0000, Cat'Killer wrote:
>>
>>> I found a way using Doug Gilbert's great sg3utils to zero all these
>>> disks in a very efficient manner, using sgp_dd, at near drive
>>> bandwidth, and proceeded to zero all the disks fully in about 4 hours!
>>>
>>> Once done, I then created a RAID 5 on 10 disks, waited for the rebuild
>>> to complete, stopped the array using mdadm, and dumped each of the
>>> RAID's components superblocks to files.
>>>
>> <-snip->
>>>
>>> The create worked fine and I waited for the rebuild to be complete
>>> before stopping the array and dumping the SBs.
>>>
>>> I then proceeded to write these same superblocks to 10 new similar
>>> disks in a different system.
>>>
>> You could just do the create with --assume-clean, which should take very
>> little time at all.  If the drives were zeroed initially then this will
>> give you valid parity data.
>>
> Thank you for this, that's exactly what I was looking for. I had
> looked in the manpage beforehand but I did not search for the right
> terms nor assumed this would work in case of an array created ontop of
> zeroed drives.
>
> Thanks again.
>
> Ben.
>
>> Cheers,
>>   Robin
>>
>> --
>>    ___           ( ' }     |       Robin Hill        <robin@robinhill.me.uk>
>> |
>>  / / )      | Little Jim says ....                            |
>>  // !!       |      "He fallen in de water !!"                 |
>>
>>
>>
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Yes, I had just come to a similar conclusion in a recent email series
and even provided a patch against the git copy of the manpage to
clarify the documentation.
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