To "hardware" RAID 5 or software RAID 5

Mike McCarty Mike.McCarty at sbcglobal.net
Thu Dec 7 22:42:30 UTC 2006


Gordon Messmer wrote:
> Robin Laing wrote:
> 
>>
>> I was looking at 5 disks minimum in the new server.  The better recovery
>> is what I am concerned with.  Just in case.  Backing up a TByte of data
>> is a pain.
> 
> 
> The probability of two simultaneous disk failures in an array that small 
> are quite small.

No, the probability of two simultaneous *independent* disc failures
is small. In areas which regularly experience brownouts simultaneous
failures have about the same probability as single failures.

>> How hard to move from RAID 5 to RAID 6 using software RAID?
> 
> 
> To the best of my knowledge, Linux doesn't offer RAID level migration. 
> You'd have to back up your data, create a new RAID device, and restore.

Or just install the new RAID and then copy the data to it.

I don't see why a level 1 array could not be extended easily.
It wouldn't even take any special software. One could just boot
from a LiveCD and use dd to create the new copy. Then inform
the RAID controller (either hard- or software) that the array
has a new disc, and you should be going. Just be sure that the
LiveCD doesn't use the swap area, or make sure the system can
avoid actually using redundancy on it.

Mike
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