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RE: RAID 5 drive replacement schedule
From: "Rivest, Philippe" <PRivest () transforce ca>
Date: Fri, 20 Jun 2008 13:24:04 -0400

Adriel & Murda

It is a security issue the way you store your data. In regards to the raid
technologies, raid 5 improves the availability of the data by making sure
that a single drive failed will not impact the availability of the data. 

Remember that security is 
1- Confidentiality
2- Availability
3- Integrity

The main goal of a Raid 5 is to help #2. You are referring to the disposal of
the HD which is the issue of confidentiality and that is not what Murda was
aiming at. If it is, go for encryption, degaussing, destruction and just
plain format (if the data is not confidential).

As I explained to him offline, the MTTF and MTBF is about the same for 2 HD
bought/constructed at about the same time. How ever, those are not absolute
numbers that state that, if one drive fails the other one is about to go too.
It's more an estimated value against which you should have some
confidence/hope, your drive should not fail before X hours (it could go
before but the average is X).

In a raid 5, Drive A, B and C are online and working (they are the same drive
bought at the same time). Drive A fails, you should NOT change drive B & C
unless they are failing also. If you do, the cost of your raid 5 will be
greater then what it should be (the replacing of the parts are going to cost
a lot). Change drive A and hope drives B & C will last longer.

The only issue is that 2 drives fail at the same time, which is very
improbable. And if it does, you should be going for your back ups.

I do hope this clarified the questions and that I wasn't to unclear with my

Merci / Thanks
Philippe Rivest, CEH
Vérificateur interne en sécurité de l'information
Courriel: Privest () transforce ca
Téléphone: (514) 331-4417

-----Message d'origine-----
De : listbounce () securityfocus com [mailto:listbounce () securityfocus com] De la
part de Adriel Desautels
Envoyé : 20 juin 2008 11:27
À : Murda Mcloud
Cc : security-basics () securityfocus com
Objet : Re: RAID 5 drive replacement schedule

        The real answer to your question is that it is very, very improbable 
that all of the drives in the array will fail at the same time. Most 
drives are good for a certain period of years, after which point you are 
getting "extra time".

        That is not a security issue though. That is an IT related issue. The

security issue comes into play when you dispose of your drives. Do you 
shred them, just throw them in the dumpster, how do you dispose of them?

        Adriel T. Desautels
        Chief Technology Officer
        Netragard, LLC.
        Office : 617-934-0269
        Mobile : 617-633-3821

        Join the Netragard, LLC. Linked In Group:

Netragard, LLC - http://www.netragard.com  -  "We make IT Safe"
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Murda Mcloud wrote:
In my mind, this a security related question as it has to do with ensuring

Does anyone have links towards any whitepapers etc that suggest replacement
of disks in a RAID 5 array as part of a maintenance cycle?

If all the drives in an array are the same age and one fails; does this
the others are more likely to fail. I'd imagine so as they have had the
amount of usage.


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