[AccessD] Google's Disk Failure Experience

jwcolby jwcolby at colbyconsulting.com
Wed Jul 21 13:14:06 CDT 2010


Yep, different needs.  But I am looking at a raid 5 like redundancy, so I get redundancy but without 
the 2X overhead.

I have to question whether the overhead of taping / cutting commercials doesn't reduce your savings 
quite a bit.  As you asked me, how much time and how do you value your time.

But that is a whole nother discussion.

John W. Colby
www.ColbyConsulting.com


Michael Bahr wrote:
> Well, I can see your point that only ripping DVD's takes 2 minutes each
> and you do not need them anymore.  But for me I record OTA/cable HD shows
> and uncut movies and cut out the commercials and archive them.  Now I have
> whole seasons worth of shows and movies.  I save money buy not buying the
> Blu-Ray disks ($30-$60 for each season or movie).  So yes it is important
> to me to have a backup as these are not reproducible.  A seperate media
> server setup as raid 1 does fit my needs.
> 
> Mike...
> 
>>  >How much is your time worth?
>>
>> This is a classic case of insufficient analysis...
>>
>> The cost is not the cost of the drive.  It is the cost of the drive (twice
>> the drives), plus the
>> cost of the SATA ports (twice) plus the cost of the power supply (twice
>> the disk current - 12v),
>> plus the cost of electricity to run the disks (twice the electricity) plus
>> the cost of a case big
>> enough to handle enough drives (twice as large disk cage) plus...
>>
>> Of course all my "twices" are on a "per disk used" basis, not a total
>> system cost and I understand
>> the difference.
>>
>> Furthermore, my time isn't the cost of my time to rip 200 dvds, it is the
>> cost of my time to rip 200
>> dvds divided by the probability of losing 2 disks at the same time.
>>
>> I ripped my drives as I wanted to watch them, so it was an incremental
>> cost accumulated over time.
>> The actual time is about 2 minutes per dvd.  200 dvds per drive is an
>> actual cost of 200 minutes to
>> fill a drive.  Would I actually rerip all of the disks?  No because many
>> of them are for my kids who
>> are now older and don't even watch those disks any more, not to mention
>> the disks I ripped that I
>> just don't care about.
>>
>> HOWEVER... In the two years that I have been using the system, I have
>> never lost one of these
>> drives.  Thus my time to "do it over again" is zero (so far).  I have been
>> working with raid
>> extensively for about 5 years, and in those 5 years I have lost single
>> drives but I have never lost
>> two drives at the same time.
>>
>> I am sure that there are numbers out there that discuss the probability of
>> two drive failures.  In
>> fact IIRC from that paper by google, the probability of failure of any
>> given single drive over 5
>> years was about 14%?  The probability of two failures (my simple math)
>> would be .14 * .14 = .0196 or
>> ~ 2%.  That is for two failures, NOT two SIMULTANEOUS failures.
>>
>> All of this matters if the cost is catastrophic.  Facing a 2% chance that
>> I will have to re-rip 200
>> dvds in any given 5 year period, I am unwilling to commit the extra money
>> to preventing this
>> possibility.
>>
>> This whole discussion does point out that an analysis of the actual
>> numbers might cause one to come
>> to a different conclusion.  And who knows, you might decide "screw the
>> costs", it is worth it to me.
>>
>> It is not worth it to me.
>>
>> Look at Unraid.
>>
>> http://lime-technology.com/
>>
>> I am not trying to sell anyone on unRaid, I am simply saying consider it
>> for a specific class of
>> redundancy needs.  For this level of redundancy need, unRaid seems like a
>> good compromise.
>>
>> John W. Colby
>> www.ColbyConsulting.com
>>
>>
>> Michael Bahr wrote:
>>> John, for your media collections you really should go only Raid 1.  Yeah
>>> if you lose the HD you can re-do everything but who has the time?
>>> Besides
>>> 2TB HD's are ~<$150 or so.  How much is your time worth?
>>>
>>> Mike...
>>>
>>>> I am about to build an UnRaid for my massive video / music collection.
>>>> I
>>>> currently have no
>>>> protection on that so if I lose a disk I lose all of that on one disk.
>>>> With Unraid I
>>>> would have "raid 5 like"
>>>> storage so that in the event of single drive failure I can still
>>>> recover.
>>>> If I do lose it I just
>>>> re-rip.  Not the end of the world but not something I want to do.
>>>>
>>>> John W. Colby
>>>> www.ColbyConsulting.com
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>>
> 
> 



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