3 ms·

Your statement was: "A RAID0 over three disks has about 1/3 the MTBF of a single disk." This is incorrect, the MTTF and MTBF are not significantly changed. A

Your statement was: "A RAID0 over three disks has about 1/3 the MTBF of a single disk." This is incorrect, the MTTF and MTBF are not significantly changed. Assuming you meant failure probability, my issue with the probability variance is the linear relationship you imply. If the variation were linear, a RAID array composed of drives with a 5% failure probability would reach certainty of failure (1.00 probability) within the interval at 20 drives. In actuality, it takes 225 drives to reach that probability. The difference is a real world consideration for capacity management. What it means is that RAID0 arrays are not as failure prone as people think they are.

moe 16y ago
> "A RAID0 over three disks has about 1/3 the MTBF of a single disk." This is incorrect, the MTTF and MTBF are not significantly changed. Wikipedia disagrees; http://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_0_failure_rate http://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_0_fai... array_MTTF = avg(drive_MTTF) / number_of_drives
- macemoneta 16y ago
  Which is at odds with the (correct) definition of MTTF as a rate-based calculation: http://en.wikipedia.org/wiki/Failure_rate http://en.wikipedia.org/wiki/Failure_rate The person that wrote the Wikipedia article you referenced read the same mythology you did; repeating it doesn't make it true. The plural of anecdote is not fact. Think about it yourself for a moment. If two cars are traveling 50mph, does that make their average speed 25mph (50/2)? Applying a divisor to a failure rate based on the number of devices is nonsensical.
  - moe 16y ago
    If you are so convinced then why don't you correct the wikipedia article? Perhaps also call up LSI and Adaptec, who use the same formula in their documentation. http://storageadvisors.adaptec.com/2005/11/01/raid-reliability-calculations/ http://storageadvisors.adaptec.com/2005/11/01/raid-reliabili... But what do they know, they only build raid controllers...
    - macemoneta 16y ago
      You're right, there's no reason to try to correct the 20% of the population that believes the Sun revolves around the Earth. It's a lost cause; you win.
      - moe 16y ago
        You're right, there's no reason to try to correct the 20% of the population Erm wait, didn't I just suggest the exact opposite? If you really think everyone has been wrong about this all the time then please, by all means, correct wikipedia or write a blog post about the matter. This "false" formula has been out there for quite some time and you find it in pretty much every write-up on the topic, including those from RAID-vendors who (I'd hope) have spent some thought on these things. On the flip-side I haven't found a single source to support your thesis. Thus I'd say the burden of proof is on you.

moe 16y ago

> "A RAID0 over three disks has about 1/3 the MTBF of a single disk." This is incorrect, the MTTF and MTBF are not significantly changed. Wikipedia disagrees; http://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_0_failure_rate http://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_0_fai... array_MTTF = avg(drive_MTTF) / number_of_drives

macemoneta 16y ago
Which is at odds with the (correct) definition of MTTF as a rate-based calculation: http://en.wikipedia.org/wiki/Failure_rate http://en.wikipedia.org/wiki/Failure_rate The person that wrote the Wikipedia article you referenced read the same mythology you did; repeating it doesn't make it true. The plural of anecdote is not fact. Think about it yourself for a moment. If two cars are traveling 50mph, does that make their average speed 25mph (50/2)? Applying a divisor to a failure rate based on the number of devices is nonsensical.
- moe 16y ago
  If you are so convinced then why don't you correct the wikipedia article? Perhaps also call up LSI and Adaptec, who use the same formula in their documentation. http://storageadvisors.adaptec.com/2005/11/01/raid-reliability-calculations/ http://storageadvisors.adaptec.com/2005/11/01/raid-reliabili... But what do they know, they only build raid controllers...
  - macemoneta 16y ago
    You're right, there's no reason to try to correct the 20% of the population that believes the Sun revolves around the Earth. It's a lost cause; you win.
    - moe 16y ago
      You're right, there's no reason to try to correct the 20% of the population Erm wait, didn't I just suggest the exact opposite? If you really think everyone has been wrong about this all the time then please, by all means, correct wikipedia or write a blog post about the matter. This "false" formula has been out there for quite some time and you find it in pretty much every write-up on the topic, including those from RAID-vendors who (I'd hope) have spent some thought on these things. On the flip-side I haven't found a single source to support your thesis. Thus I'd say the burden of proof is on you.