Boot Times, Game Loads, Cache Rolloff

Boot Times

We already know that SSHD's speed up boot times and other operations, but we've had several readers question the ability of that cached data to stay put over time. With such a small cache, the theory was that unless you are only repeating the same sort of operation, much of the advantage is not seen. Let's see how this all pans out with some attempts to observe data rolling off of the cache:

I'll walk you through this data below:

  • 1-5: Repeated reboots timed on the test bed running on a pure SSD setup.
  • 6-10: After cloning the disk to the SSHD, we timed 5 sequential reboots. The first reboot takes longest as none of the OS data has been cached. You can see boot times steadily drop to very close to SSD speeds.
  • 11-14: Battlefield 4 is installed and run for the first time (launched using string '-level Levels/SP/SP_Dam/SP_Dam' and timed from game launch until we were first allowed to 'ESC' past the level intro scene). We repeated this launch a few times to get a steady state value, and we see caching shave nearly 20 seconds off what would have been a 50+ second level load.
  • 15: We rebooted the system, noting that the reboot time returned to the uncached speed.
  • 16-18: Here we see the attempted caching of the reboot data (15) pushed some of the BF4 level data out of the cache, adding 6 seconds to the level load time on its first pass. Subsequent passes returned to the faster speeds.
  • 19-22: Here we tried a few reboot passes. This time the first reboot was not hit as hard as the previous time (15), as this time we did not install the game, but only ran it a few times.
  • 23-25: Another round of BF4 loads, effect similar to last time.
  • 26-30: Another round of reboots. This time we did a few more, as for some reason the cache did not snap back as quickly as it had on previous rounds.
  • 31-33: Final round of BF4 loads was similar to prior runs, but it appears the cache started to get a bit confused near the end, especially when looking at the weirdness that happened during the last round of reboots (26-30).

End result: 8GB of cache was not sufficient, as just launching a single game was enough activity to force previous data to be purged. Basically, doing a few other things with your PC will purge previous data out of the SSHD cache, and once you get back to the original thing (i.e. a reboot), you will mostly return to the (relatively slow) HDD performance. That reboot itself will purge some other data that was cached, so once that reboot has completed, re-launching your previous applications will also be slower than they could have been. Rinse and repeat. This effect could have been mitigated with the inclusion of a larger cache on these desktop-class devices.

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