Re: RAID-6 support in kernel?

["Jakob Østergaard" <jakob@unthought.net>]

On Mon, Jun 03, 2002 at 10:33:24AM -0700, Gregory Leblanc wrote:
> On Mon, 2002-06-03 at 02:25, Derek Vadala wrote:
>         On Mon, 3 Jun 2002, Roy Sigurd Karlsbakk wrote:
>         
>         > It'll waste 9 drives, giving me a total capacity of 7n instead of 14n. 
>         > And, by definition, RAID-6 _can_ withstand _any_ two-drive failure.
>         
>         This is certainly not true. 
>         
>         Combining N RAID-5 into a stripe wastes on N disks. 
> 
> Hot spares are quite a nice way to increase the reliability of your
> arrays, somewhat.  You can still be in trouble if a second disk fails
> before the resync finishes, but at that point you're probably talking
> about something of a more catastrophic failure, perhaps outside of the
> machine itself.  

What often happens (in my experience) is, that a number of disks build up bad
blocks.  One day, you hit one of those bad blocks, and that one disk is kicked
from the array.

When you re-sync, you *will* hit the remaining bad blocks on the other disks,
causing the array to fail completely.

Using hot-spares will "automate" this failure - meaning that an administrator
may not be anywhere near the system when this total failure happens.

Not using hot-spares is less "automatic" in the lucky case where everything
works, but it also assures that an administrator actually is near the system
when the total failure is likely to occur.

-- 
................................................................
:   jakob@unthought.net   : And I see the elder races,         :
:.........................: putrid forms of man                :
:   Jakob Østergaard      : See him rise and claim the earth,  :
:        OZ9ABN           : his downfall is at hand.           :
:.........................:............{Konkhra}...............:
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