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Renewed drives
(slrpnk.net)
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this post was submitted on 10 Jun 2024
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What is a renewed drive? Do they have a datasheet with MTBF defined?
Spinning disks, or consumable flash?
What is the use case? RAID 5? Ceph? JBOD?
What is your human capital cost of monitoring and replacing bad disks?
Let's say you have a data-lake with Ceph or something, it costs you $2-5 a month to monitor all your disks for errors, predictive failure, debug slow io, etc. The human cost of identifying a bad disk, pulling it, replacing it, then destroying it - Something like 15-30m. The cost of destroying a drive $5-50 (depending on your vendor, onsite destruction, etc)
A higher predictive failure rate of "Used" drives, has to factor in your fixed costs, and human costs. If the drive only lasts 70% as long as a new drive, then the math is fairly easy.
If the drive gets progressively slower (i.e. older SSDs) then the actual cost of the used drive becomes more difficult to model (you have to have a metric for service responsiveness, etc).
if its a hobby project, and your throwing drives into a self-healing system, then take any near free disks you can get, and just watch your power bill.
If you make money from this, or the downside of losing data is bad, then model out the higher failure rate into your cost model.