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Old 09-16-2010, 04:14 PM
T o n g
 
Default Simplest and cheapest RAID

Hi,

How practical is to create a simplest and cheapest RAID, using 2
partitions on the same disk, combining them as a RAID drive?

By "practical" I meant,

- I would assume less than 0.000001% people would do that so I can't find
any documents.

- Having 2 partitions might not give me much advantage in safety, so the
pay off is pity comparing to the hoops that I need to jump through.

As you can see, I'm still "scared" about this "complicated" RAID thing.

Any comments or inputs?

Thanks

--
Tong (remove underscore(s) to reply)
http://xpt.sourceforge.net/techdocs/
http://xpt.sourceforge.net/tools/


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Old 09-16-2010, 05:14 PM
Camaleón
 
Default Simplest and cheapest RAID

On Thu, 16 Sep 2010 16:14:53 +0000, T o n g wrote:

> How practical is to create a simplest and cheapest RAID, using 2
> partitions on the same disk, combining them as a RAID drive?
>
> By "practical" I meant,
>
> - I would assume less than 0.000001% people would do that so I can't
> find any documents.
>
> - Having 2 partitions might not give me much advantage in safety, so the
> pay off is pity comparing to the hoops that I need to jump through.
>
> As you can see, I'm still "scared" about this "complicated" RAID thing.
>
> Any comments or inputs?

Mmm, I fail to see what is the purpose of such RAID, just as an
experiment? :-?

What are your goals? With 2 disks, having a raid0/rai1 has sense when
using different devices but not the same... unless you just want to
combine them for creating a big spool/volume (JBOD), in which case, LVM
should fit better your needs.

I think more information is required :-)

Greetings,

--
Camaleón


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Old 09-16-2010, 09:57 PM
Greg Madden
 
Default Simplest and cheapest RAID

On Thursday 16 September 2010 08:14:53 T o n g wrote:
> Hi,
>
> How practical is to create a simplest and cheapest RAID, using 2
> partitions on the same disk, combining them as a RAID drive?
>
> By "practical" I meant,
>
> - I would assume less than 0.000001% people would do that so I can't find
> any documents.
>
> - Having 2 partitions might not give me much advantage in safety, so the
> pay off is pity comparing to the hoops that I need to jump through.
>
> As you can see, I'm still "scared" about this "complicated" RAID thing.
>
> Any comments or inputs?

One aspect of raid is for drive failure protection, not partition protection.
IMHO., the more spindles the better , even without using raid.
--
Peace,

Greg


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Old 09-17-2010, 12:03 AM
"Damon L. Chesser"
 
Default Simplest and cheapest RAID

On Thu, 2010-09-16 at 16:14 +0000, T o n g wrote:
> Hi,
>
> How practical is to create a simplest and cheapest RAID, using 2
> partitions on the same disk, combining them as a RAID drive?

It is not practical at all since if you loose the drive, you loose both
partition, thus defeating the purpose (0ne of them) of RAID.
>
> By "practical" I meant,
>
> - I would assume less than 0.000001% people would do that so I can't find
> any documents.
>
> - Having 2 partitions might not give me much advantage in safety, so the
> pay off is pity comparing to the hoops that I need to jump through.
>
> As you can see, I'm still "scared" about this "complicated" RAID thing.
>
> Any comments or inputs?

Having said that, it is trivial to use mdadmin to set up a raid device
of partitions on one HD. You will get a speed penalty as you are trying
to access one HD multiple times to write data or read data, but you can
do it as a training exercise to get to know the mdadmin commands. See
here: http://tldp.org/HOWTO/Software-RAID-HOWTO.html#toc6

Then, when you understand how raid works, you can take a look here:
http://wiki.tldp.org/LVM-on-RAID and figure out how to set up mdadmin to
run software raid (say 1) on which you then run lvm. The purpose? You
can add volumes to your lvm as needed, grow the fs hot and you would
need to loose several HDs before you lost your lvm.

HTH


>
> Thanks
>
> --
> Tong (remove underscore(s) to reply)
> http://xpt.sourceforge.net/techdocs/
> http://xpt.sourceforge.net/tools/
>
>


--
Damon
damon@damtek.com



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Old 09-17-2010, 02:06 AM
Doug
 
Default Simplest and cheapest RAID

On 9/16/2010 5:57 PM, Greg Madden wrote:

On Thursday 16 September 2010 08:14:53 T o n g wrote:

Hi,

How practical is to create a simplest and cheapest RAID, using 2
partitions on the same disk, combining them as a RAID drive?

By "practical" I meant,

- I would assume less than 0.000001% people would do that so I can't find
any documents.

- Having 2 partitions might not give me much advantage in safety, so the
pay off is pity comparing to the hoops that I need to jump through.

As you can see, I'm still "scared" about this "complicated" RAID thing.

Any comments or inputs?


One aspect of raid is for drive failure protection, not partition protection.
IMHO., the more spindles the better , even without using raid.


Agreed. Drives are so cheap nowadays that a real RAID is affordable to
just about anybody. Even if it had to be an external USB version.
(Says the man who isn't running one. But I do have a backup system.)
--doug


--
Blessed are the peacemakers...for they shall be shot at from both sides.
--A.M. Greeley



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Old 09-17-2010, 02:28 AM
T o n g
 
Default Simplest and cheapest RAID

First of all, thanks everyone who replied.

On Thu, 16 Sep 2010 20:03:09 -0400, Damon L. Chesser wrote:

>> How practical is to create a simplest and cheapest RAID, using 2
>> partitions on the same disk, combining them as a RAID drive?
>
> It is not practical at all since if you loose the drive, you loose both
> partition, thus defeating the purpose (0ne of them) of RAID.

Ok, seems everyone thinks this way. My justification was, HD normally not
dies all of sudden. There should be signs of failing sectors. When it
happens, I might have a better chance salvage from the other copy. Yeah,
I agree, this is cheep. :-)

> Having said that, it is trivial to use mdadmin to set up a raid device
> of partitions on one HD. You will get a speed penalty as you are trying
> to access one HD multiple times to write data or read data, but you can
> do it as a training exercise to get to know the mdadmin commands. See
> here: http://tldp.org/HOWTO/Software-RAID-HOWTO.html#toc6

Thanks -- that's exactly the kind of information that I was hoping for,
beyond just "not practical".

Thanks again for everyone who replied.

--
Tong (remove underscore(s) to reply)
http://xpt.sourceforge.net/techdocs/
http://xpt.sourceforge.net/tools/


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Old 09-17-2010, 08:52 AM
Jon Dowland
 
Default Simplest and cheapest RAID

On Fri, Sep 17, 2010 at 02:28:10AM +0000, T o n g wrote:
> Ok, seems everyone thinks this way. My justification was, HD normally not
> dies all of sudden. There should be signs of failing sectors. When it
> happens, I might have a better chance salvage from the other copy. Yeah,
> I agree, this is cheep. :-)

A total waste of time. When a drive is failing, you can't trust the data you
are reading from it.

Get a backup routine sorted.


--
Jon Dowland


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