On Fri, Apr 15, 2011 at 6:26 PM, Ross Walker <rswwalker at gmail.com> wrote: > On Apr 15, 2011, at 9:17 AM, Rudi Ahlers <Rudi at SoftDux.com> wrote: > > > > On Fri, Apr 15, 2011 at 3:05 PM, Christopher Chan <<christopher.chan at bradbury.edu.hk> > 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. > > > Put the file system's log device on it. > > -Ross > > > _______________________________________________ > Well, ZFS has a separate ZIL for that purpose, and the ZIL adds extra protection / redundancy to the whole pool. But the Cache / L2ARC drive caches all common reads & writes (simply put) onto SSD to improve overall system performance. So I was wondering if one could do this with mdraid or even just EXT3 / EXT4? -- 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/20110415/439436ee/attachment-0005.html>