Flash more reliable than hard disk?

Andrew Ku has an interesting article at Tom's Hardware showing that, despite claims by the vendors, the evidence so far available as to the reliability of flash-based SSDs in the field shows that they fail at rates comparable with hard drives. These failures have nothing to do with the limited write lifetime of flash, these are enterprise SSDs which have been in service a year or two and are thus nowhere close to their write life.

Although it is easy to believe that SSDs' lack of moving parts should make them more reliable, these results are not surprising:

• Experience shows that vendors tend to exaggerate the reliability of their products.
• Root-cause analysis of failures in hard-drive systems shows that 45-75% of failures are not due to the disks themselves, so that even if SSDs were a lot more reliable that hard drives but were used in similar systems, the effect on overall system reliability would be small. In fact, most of the SSDs surveyed were used in hybrid systems alongside disks.
• The flash SSDs have even more software embedded in them than disk drives. Thus even if their raw storage of bits was more reliable than the disk platters, they would be more vulnerable to software errors.

These are early days for the kinds of mass deployments of SSDs that can generate useful data on field reliability, so there is no suggestion that they should be avoided. The article concludes:

The only definitive conclusion we can reach right now is that you should take any claim of reliability from an SSD vendor with a grain of salt.

"Paying for Long-Term Storage" Revisited

In this comment to my post onPaying for Long-Term Storage I linked to this speech by Andrew Haldane and Richard Davies of the Bank of England. They used historical data from 624 UK and US companies to estimate the extent to which short-term thinking is reflected in the prices of their stock. In theory, the price of each company's stock should reflect the net present value of the stream of future dividends. They find that:

First, there is statistically significant evidence of short-termism in the pricing of companies’ equities. This is true across all industrial sectors. Moreover, there is evidence of short-termism having increased over the recent past. Myopia is mounting. Second, estimates of short-termism are economically as well as statistically significant. Empirical evidence points to excess discounting of between 5% and 10% per year.

In other words, the interest rate being charged when using standard discounted cash flow computations to justify current investments is systematically 5-10% too high, resulting in investments that would be profitable not being made.

This is obviously a serious problem for all efforts to preserve content for future readers; the value the content eventually delivers to the future readers has to be enormous to justify even minimal investment now in preserving it. Below the fold I describe how even this analysis fails to capture the scale of the problem of short-termism.