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Re: [HELP] RAID chunk-size - alternatives

Since I'm feeling bored at the moment...

On Tue, Apr 02, 2002 at 02:29:28PM -0800, Alvin Oga wrote:
> typically a minimum of 2 disks used for raid0 or raid1...
> 	raid1(mirroring) protects against one disk failure
> 	( one disk's capacity is used as a redundant copy and not for user)
> 		( 50% lost of space )

Correction:  Protects against loss of all-but-one disks.  A 10-way
mirror can drop 9 disks without losing any data.

> 	raid0(stripping) does not help for disk failures

A stripe set is more vulnerable to disk failure than a non-RAID
solution.  If you're not using RAID, a failed drive only takes out
the data on that one disk.  With RAID0, a failed drive will cost you
most (if not all) of the data on the array.

> typically 5 disks for raid5 ... 
> 	( 3 disks mininum -- 1/3 of your disks lost to parity
> 	( 4 disks .......... 1/4 of your disks lost to parity
> 	( 5 disks .......... 1/5 of your disks lost to parity

Don't know where you got the "typically 5 disks" bit from.  RAID5
costs you one drive's worth of capacity.  Also, if I were to set up a
5-disk RAID5 for critical data, I'd go with 4 active disks, plus one

> typically raid01 - needs 4 disks ...
> 	first data is stripped across 2 disks than its mirrored to 2 more disks
> 	- due to mirroring... 2 disks is lost for "mirror"

Minimum 4 disks, but any larger even number of active disks will work.
Here again, if dealing with important data, I'd add an odd disk to the
array as a spare.

> and after its all said and done... pull out a disk (simulated disk crash)
> and see if you're data is still intact

Yep.  It's the only way to be sure.

When we reduce our own liberties to stop terrorism, the terrorists
have already won. - reverius

Innocence is no protection when governments go bad. - Tom Swiss

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