On Fri, Apr 15, 2011 at 3:05 PM, Christopher Chan < christopher.chan at bradbury.edu.hk> wrote: > On Friday, April 15, 2011 07:24 PM, Benjamin Franz wrote: > > On 04/14/2011 09:00 PM, Christopher Chan wrote: > >> > >> Wanna try that again with 64MB of cache only and tell us whether there > >> is a difference in performance? > >> > >> There is a reason why 3ware 85xx cards were complete rubbish when used > >> for raid5 and which led to the 95xx/96xx series. > >> _ > > > > I don't happen to have any systems I can test with the 1.5TB drives > > without controller cache right now, but I have a system with some old > > 500GB drives (which are about half as fast as the 1.5TB drives in > > individual sustained I/O throughput) attached directly to onboard SATA > > ports in a 8 x RAID6 with *no* controller cache at all. The machine has > > 16GB of RAM and bonnie++ therefore used 32GB of data for the test. > > > > Version 1.96 ------Sequential Output------ --Sequential Input- > > --Random- > > Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- > > --Seeks-- > > Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP > > /sec %CP > > pbox3 32160M 389 98 76709 22 91071 26 2209 95 264892 26 > > 590.5 11 > > Latency 24190us 1244ms 1580ms 60411us 69901us > > 42586us > > Version 1.96 ------Sequential Create------ --------Random > > Create-------- > > pbox3 -Create-- --Read--- -Delete-- -Create-- --Read--- > > -Delete-- > > files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP > > /sec %CP > > 16 10910 31 +++++ +++ +++++ +++ 29293 80 +++++ +++ > > +++++ +++ > > Latency 775us 610us 979us 740us 370us > > 380us > > > > Given that the underlaying drives are effectively something like half as > > fast as the drives in the other test, the results are quite comparable. > > Woohoo, next we will be seeing md raid6 also giving comparable results > if that is the case. I am not the only person on this list that thinks > cache is king for raid5/6 on hardware raid boards and the using hardware > raid + bbu cache for better performance one of the two reasons why we > don't do md raid5/6. > > > > > > Cache doesn't make a lot of difference when you quickly write a lot more > > data than the cache can hold. The limiting factor becomes the slowest > > component - usually the drives themselves. Cache isn't magic performance > > pixie dust. It helps in certain use cases and is nearly irrelevant in > > others. > > > > Yeah, you are right - but cache is primarily to buffer the writes for > performance. Why else go through the expense of getting bbu cache? So > what happens when you tweak bonnie a bit? > _______________________________________________ > > As matter of interest, does anyone know how to use an SSD drive for cach purposes on Linux software RAID drives? ZFS has this feature and it makes a helluva difference to a storage server's performance. -- Kind Regards Rudi Ahlers SoftDux Website: http://www.SoftDux.com Technical Blog: http://Blog.SoftDux.com Office: 087 805 9573 Cell: 082 554 7532 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.centos.org/pipermail/centos/attachments/20110415/92943df2/attachment-0003.html>