On Fri, Dec 06, 2013 at 03:24:18AM -0600, Stan Hoeppner wrote: > On 12/5/2013 1:24 PM, Piergiorgio Sartor wrote: > > > The "stripe_cache_size" was set to the max 32768. > > You don't want to set this so high. Doing this will: > > 1. Usually decrease throughput > 2. Eat a huge amount of memory. With 5 drives: > > ((32768*4096)*5)/1048576 = 640 MB RAM consumed for the stripe buffer > > For 5 or fewer pieces of spinning rust a value of 2048 or less should be > sufficient. Test 512, 1024, 2048, 4096, and 8192. You should see your > throughput go up and then back down. Find the sweet spot and use that > value. If two of these yield throughput within 5% of one another, use > the lower value as it eats less RAM. Hi Stan, thanks for the reply, I was looking forward to it, since you always provide useful information. I checked two systems, one, different, with RAID-5, the other the actual RAID-6. In the first one, 2048 seems to be the best stripe cache size, while more results in slower writing speed, albeit not too much. For the RAID-6, it seems 32768 is the best value. There is one difference, the RAID-5 has chunk size of 512k (default), while the RAID-6 has still the 64k. BTW, why is that? I mean why large stripe cache results in lower writing speed? Thanks, bye, -- piergiorgio -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
