French-Guy Posted December 5, 2017 Author Share Posted December 5, 2017 What minimum CPU would be necessary to run a dual parity disk in good conditions? Quote Link to comment
Frank1940 Posted December 5, 2017 Share Posted December 5, 2017 If you are still running that sempron, the parity check time will approximately double. (I had a dual parity setup on my test bed server -- running a sempron 140 back when dual parity was first introduced.) If my memory is not playing tricks with me, I seem to recall that Intel chips preformed a bit better than AMD. I also seem to recall that a CPU had to have around 2000 passmarks to eliminate the time differential between dual and single parity. Be a bit careful as the passmarks available for each core is a factor as I believe that the parity operation is single threaded. 1 Quote Link to comment
French-Guy Posted December 5, 2017 Author Share Posted December 5, 2017 I didn't purchase that FX-8320e finally.............was too busy at work, and couldn't go to my Microcenter on time to get it for $40 ! Anyway, I have a AMD X2 250 with 4GB memory doing nothing, so i will do some tests. It won't be a huge improvement of course, but still better than my current Sempron Will see how the parity check improves on my current server (just 1 parity drive, but it took a looooooong time with my Sempron !!!) And I'll keep an eye on some good deals for Christmas Quote Link to comment
JorgeB Posted December 5, 2017 Share Posted December 5, 2017 56 minutes ago, French-Guy said: What minimum CPU would be necessary to run a dual parity disk in good conditions? Any Sandybridge or newer Celeron/Pentium is enough for a small/medium array. Quote Link to comment
French-Guy Posted December 5, 2017 Author Share Posted December 5, 2017 Was just looking at Microcenter for their weekly ads, and saw this: AMD FX 8320e + ASUS M5A78L-M Plus/USB3 AM3+ = $50 after rebates !!! Quote Link to comment
dchamb Posted December 5, 2017 Share Posted December 5, 2017 1 hour ago, Frank1940 said: No. Parity 1 is a very simple binary operation. Parity 2 is a complex matrix operation and is very CPU intensive UNLESS you have a newer CPU which has an new operator which reduces the number of CPU cycles to do the calculations. You can ANY two drives fail and not lose data. That includes both parity and data drives. So you can have two data drives fail, a data and parity drive, or a two parity drives fail without data loss. But if a third drive fails with any of these combinations, you will be losing data! Thanks Frank1490, Is there a document somewhere that describes how the second parity algorithm works? My unRAID server uses an Intel i5-3570. I'm pretty sure I'm covered. Dale Quote Link to comment
Frank1940 Posted December 5, 2017 Share Posted December 5, 2017 8 minutes ago, dchamb said: Is there a document somewhere that describes how the second parity algorithm works? Start here: https://forums.lime-technology.com/topic/49598-unraid-server-release-620-rc4-available/#comment-487759 and google Q parity calculation and the papers that you find are not for the faint of heart. The theory behind the whole thing involves a lot of matrix algebra. (I hold a BSEE degree from many, many years ago and I when I was looking at the mathematical basis for this approach I soon realize how little I remember from my college years!) Quote Link to comment
bonienl Posted December 5, 2017 Share Posted December 5, 2017 If you are in mathematics, see this paper. p+q, raid6.pdf 1 Quote Link to comment
pwm Posted December 5, 2017 Share Posted December 5, 2017 The math for second/third/fourth/... parity is normally only covered in quite high-end math-specific courses. Anyway - if you think it was slow to compute the parity for the first drive, then it was because of the capability of the machine to read/write all the data. Even slow processors can compute XOR at a number of GB/second so it's the disk transfer rates that decides the time. When adding additional parity disks, then the CPU time for parity computation starts to affect the total parity build time. The algorithms to compute parity is similar to what is used in normal software RAID on Linux or what is used by Snapraid etc. And it's the same algorithms as computed by dedicated RAID controller cards. Quote Link to comment
French-Guy Posted December 5, 2017 Author Share Posted December 5, 2017 That's funny........Did you know that Galois was a French mathematician, born in 1811??? Quote Link to comment
pwm Posted December 5, 2017 Share Posted December 5, 2017 3 minutes ago, French-Guy said: That's funny........Did you know that Galois was a French mathematician, born in 1811??? Yes, but then quite few people learns enough math to reach into 19th and 20th century math. There are a few exceptions where some reasonably simple concepts was discovered rather late. Quote Link to comment
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