Secrets about SSDs: the thermal issue

Yesterday I bought a Kingston V+ SSD (128GB), pretty much one of the fastest solid state drives on the market (among others of the same size).

Now, SSDs are great, I don’t regret buying it because it’s really really fast. But here’s a relevant thing that I noticed which did not appear in any of the reviews around the internet and I would like people to know.

Premise: I installed it  in my samsung Q70 laptop (2 years old, 2.0GHz core 2 duo).

The Thermal issue

This is what you read from all technical reviews about how good SSDs are and what enormous advantages they represent:

Hard disk IO is nowadays the worst bottleneck for our evoluted super fast CPUs. Modern processors have to put themselves to sleep for relatively enormous amount of time, waiting for disk IO to happen.

And that’s definitely true, it’s such a pity our processor could run a heavy encoding algorithm with a crazy bandwidth, but it needs to face the miserable 25-30MB/s of spinning platters hard disks.

But what happens if hard disks suddenly become 10 times faster?
Automatic installers will go very fast, moving files here and there is awesome, booting takes 1/3 of the time. That’s true. On the other hand, your CPU average operating  temperature will definitely raise. Let’s see why this thermal issue makes dramatically perfect sense:

Let’s imagine we need to uncompress 1GB compressed file. Your archiving application will probably perform a tight cycle over each chunk of file:

1. read from arhive (disk IO),
2. uncompress/dictionary lookup/CRC (CPU computing)
3. write to uncompressed file (disk IO)

In the HDD case

We just said that CPU operations are way faster than disk IOs. Let’s guess computing a data chunk is just even 2 orders of magnitude faster than reading or writing it to disk.

Ratio: CPU time / Disk IO time = 10/2*10^3 = 0,02

This translates like: with all given approximations, CPU is actually computing 2% of the time.

In the SSD case

In my case, with SSD adoption I achieved almost exactly 10x disk IO speed. Given the loose hypothesys of the above paragraph, this means that CPU is faster than disk IO just of 1 order of magnitude.

Ratio: CPU time / Disk IO = 10/2*10^2 = 0,2

With disk IO speed boost of SSD, the CPU is busy for the 20% of the time.

Conclusion

With 10 times faster disk IO, we expect that during a simple file uncompression (running any autoinstaller) CPU is computing 10 times more intensely. And this will impact on the thermal balance of your computer. Quite much.

Of course handling of compressed files is just an example. As far as now, I noticed this behaviour coming visibly up also after rebooting.
This si really something that you don’t ever think about before you face it. That is also because SSDs keep pretty fresh because of their power efficiency. Thus seems so far from the excited mind of  the pre-buyer’s that he’ll occur in excessive heat issues.

In my specific test looks like the CPU is behaving like a real bottleneck uncompressing a big LZMA archive (7z). CPU was stuck to 100% on BOTH cores during the process (which – ok – was happening really fast).