Guess the size of a RAID{5,6} device

Guess the size of a RAID{5,6} device

[Francis Moreau]

Hello,

I'd like to know if it's possible to get the size of a RAID{5,6} which
is not created yet but the size of the partitions which will make up the
array are.

Thanks

Re: Guess the size of a RAID{5,6} device

[NeilBrown]

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On Fri, 11 Apr 2014 10:19:23 +0200 Francis Moreau <francis.moro@gmail.com>
wrote:

> Hello,
> 
> I'd like to know if it's possible to get the size of a RAID{5,6} which
> is not created yet but the size of the partitions which will make up the
> array are.

How precise does the "guess" need to be?

If you subtract about 128Meg from the size of the partitions, round down the
a multiple of the chunk size then multiply by the number of data disks, you
should come quite close.

If you want an exact number, then you really need to create the array.

NeilBrown


> 
> Thanks
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Re: Guess the size of a RAID{5,6} device

[Francis Moreau]

Hello Neil,

On 04/12/2014 01:50 AM, NeilBrown wrote:
> On Fri, 11 Apr 2014 10:19:23 +0200 Francis Moreau <francis.moro@gmail.com>
> wrote:
> 
>> Hello,
>>
>> I'd like to know if it's possible to get the size of a RAID{5,6} which
>> is not created yet but the size of the partitions which will make up the
>> array are.
> 
> How precise does the "guess" need to be?
> 

I just need an approximation in order to report to user some information
about the (raided) partition my tool is about to create.

> If you subtract about 128Meg from the size of the partitions, round down the

Just to be sure the size of the partitions is equal to the min size of
all partitions ?

> a multiple of the chunk size then multiply by the number of data disks, you
> should come quite close.

Thanks, that should do the trick.

Re: Guess the size of a RAID{5,6} device

[NeilBrown]

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On Sat, 12 Apr 2014 10:12:00 +0200 Francis Moreau <francis.moro@gmail.com>
wrote:

> Hello Neil,
> 
> On 04/12/2014 01:50 AM, NeilBrown wrote:
> > On Fri, 11 Apr 2014 10:19:23 +0200 Francis Moreau <francis.moro@gmail.com>
> > wrote:
> > 
> >> Hello,
> >>
> >> I'd like to know if it's possible to get the size of a RAID{5,6} which
> >> is not created yet but the size of the partitions which will make up the
> >> array are.
> > 
> > How precise does the "guess" need to be?
> > 
> 
> I just need an approximation in order to report to user some information
> about the (raided) partition my tool is about to create.
> 
> > If you subtract about 128Meg from the size of the partitions, round down the
> 
> Just to be sure the size of the partitions is equal to the min size of
> all partitions ?

Correct.

NeilBrown


> 
> > a multiple of the chunk size then multiply by the number of data disks, you
> > should come quite close.
> 
> Thanks, that should do the trick.


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