Re: SSD TBW

Lawrence D’Oliveiro <[email protected]> wrote:
|----------------------------------------------------------------------|
|"I found out that a common measure of the projected life of an SSD is |
|being given in units of “terabytes written” (TBW). This will typically|
|be much larger than the capacity of the drive itself, because it      |
|includes the sum total of all write operations on the drive, including|
|deletion of data.                                                     |
|                                                                      |
|For example, a 1-terabyte drive could have an expected figure of      |
|merit, by this measure, of 1000TBW -- that means it should be able to |
|endure a total of a petabyte (1000 terabytes) written to it before    |
|showing signs of failure.                                             |
|                                                                      |
|But it seems to me, a 2-terabyte drive made of parts with the same    |
|quality, meaning each storage cell has the same expected endurance as |
|before, should have a proportionately greater figure of merit, namely |
|2000TBW.                                                              |
|                                                                      |
|But the bigger drive will likely not last longer than the smaller one |
|-- unless you don’t actually make use of the extra space.             |
|                                                                      |
|So why not divide the TBW by the actual capacity of the drive? Then   |
|you end up with a ratio of how much can be written in total, to the   |
|drive capacity -- call it, say, the “cumulative write ratio”. Both    |
|those drives would have a cumulative write ratio of 1000.             |
|                                                                      |
|That number, it seems to me, correlates better to the overall quality |
|of the unit than TBW does. E.g. if you see a bigger drive with a      |
|smaller cumulative write ratio, you can suspect that they are cutting |
|corners somewhere to keep the cost down."                             |
|----------------------------------------------------------------------|

I do not yet have a first-hand experience of an SSD failure. Don Y
complains in news:sci.electronics.design that an SSD suddenly
completely failed, instead of gradual partial degradations of a hard
disk. What does Lawrence D’Oliveiro mean by
"before
showing signs of failure."?
This quotation gave me the impression that Lawrence D’Oliveiro does
not expect the dramatic all-or-nothing scenario that Don Y reported.

This is a crosspost to news:sci.electronics.design
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