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RE: RAID 5 drive replacement schedule
From: "Petter Bruland" <pbruland () fcglv com>
Date: Fri, 20 Jun 2008 12:29:20 -0700

Security or not...

Does your array support a hot-spare or stand-by disk? Then that would be the best way to go. Once a drive fails, it 
will alert based on syslog/eventlog/3rd party app etc that a drive is bad, and rebuild the bad drive's data on the 
hot-spare/stand-by disk.

If that isn't an option, and you are expecting a failure any day, I'd just keep an eye on the array health and make 
sure you have one or two spare drives on hand.

** I've never done this, but I believe you can slowly replace all drives, and then have a working full RAID-5 disk set 
as a backup?  I have had bad luck with older drives that used to be 24/7, then taken offline and back online.

Those are my 2 cents.... And in today's exchange rate, that's not much.

-Petter



-----Original Message-----
From: listbounce () securityfocus com [mailto:listbounce () securityfocus com] On Behalf Of Adriel Desautels
Sent: Friday, June 20, 2008 11:00 AM
To: Rivest, Philippe
Cc: Murda Mcloud; security-basics () securityfocus com
Subject: Re: RAID 5 drive replacement schedule

Philippe,
        I disagree with you and I think that the definition of security that you provided is partial, but thats just my 
opinion. Availability is a vague term that can, but does not always have a role in security. 
Determining what the proper schedule is for a drive replacement policy is something that can be done by IT without the 
security team. Deciding how to dispose of the drives on the other hand is security.


Regards,
        Adriel T. Desautels
        Chief Technology Officer
        Netragard, LLC.
        Office : 617-934-0269
        Mobile : 617-633-3821
        http://www.linkedin.com/pub/1/118/a45

        Join the Netragard, LLC. Linked In Group:
        http://www.linkedin.com/e/gis/48683/0B98E1705142

---------------------------------------------------------------
Netragard, LLC - http://www.netragard.com  -  "We make IT Safe"
Penetration Testing, Vulnerability Assessments, Website Security

Netragard Whitepaper Downloads:
-------------------------------
Choosing the right provider : http://tinyurl.com/2ahk3j Three Things you must know  : http://tinyurl.com/26pjsn


Rivest, Philippe wrote:
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 details!

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


-----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

Murda,
      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?

      
Regards,
      Adriel T. Desautels
      Chief Technology Officer
      Netragard, LLC.
      Office : 617-934-0269
      Mobile : 617-633-3821
      http://www.linkedin.com/pub/1/118/a45

      Join the Netragard, LLC. Linked In Group:
      http://www.linkedin.com/e/gis/48683/0B98E1705142

---------------------------------------------------------------
Netragard, LLC - http://www.netragard.com  -  "We make IT Safe"
Penetration Testing, Vulnerability Assessments, Website Security

Netragard Whitepaper Downloads:
-------------------------------
Choosing the right provider : http://tinyurl.com/2ahk3j Three Things 
you must know  : http://tinyurl.com/26pjsn


Murda Mcloud wrote:
In my mind, this a security related question as it has to do with 
ensuring availability.

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
mean
the others are more likely to fail. I'd imagine so as they have had 
the
same
amount of usage.





 



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