Data Sheet

17
6. Technology Term Explanations
6.1 TBW
Terabytes Written (TBW) directly measures how much you can write cumulatively into the drive over its
lifetime. Essentially, it just includes the multiplication we did above in the measurement itself.
For example, if your drive is rated for 365 TBW, that means you can write 365 TB into it before you may
need to replace it.
If its warranty period is 5 years, that works out to 365 TB ÷ (5 years × 365 days/year) = 200 GB of writes per
day. If your drive was 200 GB in size, that’s equivalent to 1 DWPD. Correspondingly, if your drive was rated
for 3.65 PBW = 3,650 TBW, that works out to 2 TB of writes per day, or 10 DWPD.
As you can see, if you know the drive’s size and warranty period, you can always get from DWPD to TBW or
vice-versa with some simple multiplications or divisions. The two measurements are really very similar.
6.2 DWPD
Drive Writes Per Day (DWPD) measures how many times you could overwrite the drive’s entire size each
day of its life. For example, suppose your drive is 200 GB and its warranty period is 5 years. If its DWPD is 1,
that means you can write 200 GB (its size, one time) into it every single day for the next five years.
If you multiply that out, that’s 200 GB per day × 365 days/year × 5 years = 365 TB of cumulative writes
before you may need to replace it.
If its DWPD was 10 instead of 1, that would mean you can write 10 × 200 GB = 2 TB (its size, ten times) into
it every day. Correspondingly, that’s 3,650 TB = 3.65 PB of cumulative writes over 5 years.
6.3 MTBF Telcordia SR-332
MTBF (mean time between failures) is a measure of how reliable a hardware product or component is. For
most components, the measure is typically in thousands or even tens of thousands of hours between
failures. For example, a SSD may have a mean time between failures of 200,000 hours. A desired MTBF can
be used as a quantifiable objective when designing a new product. The MTBF figure can be developed as
the result of intensive testing, based on actual product experience, or predicted by analyzing known factors.
The manufacturer may provide it as an index of a product's or component's reliability and, in some cases,
to give customers an idea of how much service to plan for. In Transcend MTBF data, we use Telcordia
SR-332 Issue 4 method to do estimated calculation.