Thread out. Kind regards
Paul Wilkins On Thu, 22 Aug 2019 at 14:12, Matthew Moyle-Croft <[email protected]> wrote: > I preface this by saying - “I recommend that all my competitors spend > their engineering time and effort on solving for this problem”. > > > 3 - If we figure a drive is good for 1M restarts, then you'd expect > precession to cause 0.2% of disks to fail over a 5 year lifespan > > So, let’s look at the Backblaze numbers ( > https://www.backblaze.com/blog/2018-hard-drive-failure-rates/). Their DCs > are in LA and AZ are approximately as north as Adelaide and Sydney are > south. > > They see a 1.27% Annual failure rate across their fleet. If you look at > their numbers the variation is by far due to the model than anything else. > If you’re claiming 0.2% over FIVE years (ie. not annually but across 5 > years), as before, this isn’t going to be a significant impact to the > fleet. It’s also worth noting that they don’t seem to look at controller > failure vs mechanical failure. > > An extra 40 drives per year against 4455 failures per annum. 40 drives per > annum is around USD$8k ($200/drive at scale). If you said to BackBlaze, I’d > like to save you $8k, but you’ve got to spend a few million to realign the > racks, then, well, it’s not going to be a business case I’d defend. (Mostly > cost would be rebuilding the DCs so the cooling was arranged properly as > well as all the cabling, hot aisle containment etc etc). > > At 0.2% across 5 years you’d have to have more than 1000 drives to make > this something worth caring about (1000 drives means 2 extra failed drives > over 5 years). > > > 4 - Whether this shows up in MTBF depends on measurement techniques, and > whether the effect is above the random noise > > See above. > > Feel free to argue how I’ve butchered probability etc, but I doubt it > makes the business case “better”. > > MMC
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