[rcthompson]

If hard drives increase in capacity while maintaining the same MTBF, does this count as an improvement? If you previously stored your data on 10 drives and now you can store the same data on 5 drives, that reduces the probability of failure of the system as a whole, right? Is there some kind of "failure rate per byte" measure that normalizes for this?

[Retric]

It depends on what you’re doing and what you’re concerned about.

For a simplified example suppose you have X drives storing 20TB vs 2X drives with 10TB in a simple RAID 1 configuration. When a drive fails there’s a risk period before its contents are replicated on another drive. At constant transfer speeds larger disks double that period per drive but half the number of failures. Net result the risk is identical in both setups.

However, that assumes a constant transfer speeds, faster transfer rates reduce overall risks.

[rcthompson]

Hmm, I hadn't considered that doubling the drive size doubles the resilver time and therefore doubles the exposure time for risk of array loss. I guess the math gets complicated depending on RAID topology.

[hbn]

> If you previously stored your data on 10 drives and now you can store the same data on 5 drives, that reduces the probability of failure of the system as a whole, right?

Well it also means in the case of failure you get 2x the spread of damage across the same amount of data

[Chiron1991]

I don't know about this exact metrics, but the Backblaze hard drive report is always a very good read when thinking about failure rates. Maybe check it out and see if you'll get your answers there.