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> If one SSD has a failure rate of 5%, 4 SSDs will have a failure rate of 18.6% That doesn't make sense, the probability that all 4 SSDs will simultaneously f
by melony 4y ago
> If one SSD has a failure rate of 5%, 4 SSDs will have a failure rate of 18.6%
That doesn't make sense, the probability that all 4 SSDs
will simultaneously fail at any given moment, assuming a uniform distribution, is p(0.05)^4.
- yurishimo 4y agoYou don't need all 4 to fail, you need one, assuming no redundancy, but then you are sacrificing space, thus requiring you to buy even more drives.
- LionTamer 4y agoIf only one drive fails why would you lose all your data?
- Dylan16807 4y agoWe're trying to avoid losing any data here. So we desperately need a parity drive, which will bring the odds of data loss down to 2.3% for 4+1. (Though there are other factors that significantly complicate these odds.)
- ehzy 4y agoThe point is to not lose any data. In the example, if you need 4 drives to store 16 TB of data instead of 1, your probability of data loss is 18.6% vs 5%.
- matheweis 4y agoIn theory but not necessarily in practice (see the 40k hr SSD firmware bug that recently took out HN)