Re: nested raid possible?

turbo@weasel.com un jour écrivit:

I have a raid-5 array of six 250gb hard drives.
I just bought four 500gb hard drives.

I know I can take the six drives and make three raid-1 arrays of 500gb.

   Here, you probably means three RAID-0 arrays of 500GB, otherwise you 
would get three RAID-1 of 250GB.

After doing that, can I make a raid-5 array consisting of the three 
raid-0 arrays, and the four 500gb hard drives?

   Yes, It would works, because all you need is to get a block device. 
Software Raid takes many block devices to generate one block device, so It 
is transparent.

   That said, I don't say that It is a good idea to do It as you are 
suggesting.  You realize that It would be less reliable than a RAID-5 
array made of seven 500GB drive.

   If you really want to do than, I would feel more confident using 
RAID-6.   Another option is to use RAID-10 with 4x250GB with 2 hot spare, 
and connect everything in a RAID-5 array for a total of also 2.5TB of 
usable space.  Personnaly, considering the price of the hard drives, I 
won't ever bother and use only 500GB drive.

   That said, It is your data.  It is you that know if It is better to 
have the full 3TB, at the cost of somewhat more risk to loose your data. 
Maybe the additional risk is low enough for your needs, I don't know.

   But in a business environment, I would normaly not do It.

Simon Valiquette

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