On Wed, Nov 20, 2013 at 9:25 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > Some SSD's are also claim the ability to flush the cache on power loss: > > http://www.intel.com/content/www/us/en/solid-state-drives/ssd-320-series-power-loss-data-protection-brief.html > > Which should in theory let them respond immediately to flush requests, > right? Except they only seem to advertise it as a safety (rather than a > performance) feature, so I probably misunderstand something. > > And the 520 doesn't claim this feature (look for "enhanced power loss > protection" at http://ark.intel.com/products/66248), so that wouldn't > explain these results anyway. FYI, nowhere does Intel imply that the CMD_FLUSH is instantaneous. The product brief for Intel 320 SSDs (above link), explains that it is implemented by a power-fail detection circuit that detects drop in power-supply, following which the on-disk controller issues an internal CMD_FLUSH equivalent command to ensure data is moved to the non-volatile area from the disk-cache. Large secondary capacitors ensure backup supply for this brief duration. Thus applications can always perform asynchronous I/O upon the disk, taking comfort in the fact that the physical disk ensures that all data in the volatile disk-cache is automatically transferred to the non-volatile area even in the event of an external power-failure. Thus the host never has to worry about issuing a CMD_FLUSH (which is still a terribly expensive performance bottleneck, even on the Intel 320 SSDs). -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
