On 3/4/06, Steve Byan <[EMAIL PROTECTED]> wrote: > On Mar 4, 2006, at 2:10 PM, Jeff Garzik wrote: > > Measurements on NCQ in the field show a distinct performance > > improvement... 30% has been measured on Linux. Nothing to sneeze at. > > Wow! 30% is amazing. I'd be interested in knowing how the costs break > down; are these measurements published anywhere?
Full-stroke random reads with small operations (4k or less) typically show 75-85% performance improvement, from the ability of a 7200rpm drive to carve 4ms out of their response time, as well as a huge chunk of seek distance. Random writes, since as you said they're already reordered with cache enabled, don't typically show any sort of increase in desktop applications. NCQ FUA writes or NCQ writes with cache disabled should show the same ballpark performance improvement as random reads in saturated workloads. Again however, this is for the full-stroke random case. Local area workloads need to be analyzed more thoroughly, and may differ in performance gain by manufacturer. --eric - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
