May 9, 200818 yr Just a status update. Recently I had recompiled the kernel for PAE to allow use of all available memory on my machine. I've filled all 4 slots with 2GB chips and have 8GB memory available to the kernel now. Through all readings, enabling PAE comes with a performance hit. I figured CPU utilization in unraid is very low so the hit would not be that bad. My goal was to keep the directory inodes in memory as long as possible. I've been running in PAE mode for weeks now and today I did a test whereby I downloaded a huge rar unrared it then did an FC to the same thing on another 4GB unraid server. on the 8GB unraid server after unraring everything here is the memory utilization top - 08:26:19 up 20:57, 3 users, load average: 0.00, 0.03, 0.00 Tasks: 77 total, 1 running, 76 sleeping, 0 stopped, 0 zombie Cpu(s): 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 8309156k total, 7204580k used, 1104576k free, 172212k buffers Swap: 262136k total, 0k used, 262136k free, 6740484k cached I reran the slocate program which scans all files and directories afterward and it ran in seconds without accessing the disk. In contrast on the 4GB machine it spun up the unused disks. (as expected). Then from an XP machine I opened a cmd box and did an FC from one machine to the other to insure they were exact. (the 4G machine was populated separately from the source and unrared separately) I'm happy to report everything compared 100% CPU utilization was farily low. I did not see significant issues with data delivery, then again, my network is not a top speed network. Therefore I cannot vouch for it's performance on a network where you are streaming HD to it (from it should not be a problem). This will have to be tested by someone else. This test does prove that there are no issues with unraid, the kernel and PAE in average usage. Nothing bombed, no core dumps and no binary differences. Good so far. U:\Videos\TV\V>dir Volume in drive U is disk2 Volume Serial Number is 0879-0102 Directory of U:\Videos\TV\V 05/09/2008 01:13 PM <DIR> . 05/09/2008 01:13 PM <DIR> .. 11/28/2005 06:33 PM 666,605,056 (TV) V The Final Battle 1.avi 11/28/2005 08:28 PM 680,482,304 (TV) V The Final Battle 2.avi 11/28/2005 10:15 PM 627,540,992 (TV) V The Final Battle 3.avi 11/26/2005 05:37 PM 777,868,800 (TV) V The Mini Series 1.avi 11/26/2005 06:29 PM 674,839,040 (TV) V The Mini Series 2.avi 5 File(s) 3,427,336,192 bytes 2 Dir(s) 365,408,976,896 bytes free U:\Videos\TV\V>for %1 in (*.avi) do fc /b "U:%1" "f:%1" U:\Videos\TV\V>fc /b "U:(TV) V The Final Battle 1.avi" "f:(TV) V The Final Battle 1.avi" Comparing files U:(TV) V The Final Battle 1.avi and F:(TV) V THE FINAL BATTLE 1.AVI FC: no differences encountered U:\Videos\TV\V>fc /b "U:(TV) V The Final Battle 2.avi" "f:(TV) V The Final Battle 2.avi" Comparing files U:(TV) V The Final Battle 2.avi and F:(TV) V THE FINAL BATTLE 2.AVI FC: no differences encountered U:\Videos\TV\V>fc /b "U:(TV) V The Final Battle 3.avi" "f:(TV) V The Final Battle 3.avi" Comparing files U:(TV) V The Final Battle 3.avi and F:(TV) V THE FINAL BATTLE 3.AVI FC: no differences encountered U:\Videos\TV\V>fc /b "U:(TV) V The Mini Series 1.avi" "f:(TV) V The Mini Series1.avi" Comparing files U:(TV) V The Mini Series 1.avi and F:(TV) V THE MINI SERIES 1.AVI FC: no differences encountered U:\Videos\TV\V>fc /b "U:(TV) V The Mini Series 2.avi" "f:(TV) V The Mini Series2.avi" Comparing files U:(TV) V The Mini Series 2.avi and F:(TV) V THE MINI SERIES 2.AV I FC: no differences encountered
May 9, 200818 yr Nice work WeeboTech! I wonder if you know the answer to this: If PAE is enabled in the kernel, but there is 4GB or less memory actually installed, does the kernel still use PAE? Similarly, if the PAE is enabled in the kernel, but the h/w does not support PAE, but there is also not more than 4GB memory, will it still work? This is why we haven't enabled PAE in stock unRAID kernel - because enabling it is a compile-time option and I don't know if it will not run on some user's existing h/w - I guess we can try it and find out Another possibility is to produce 2 bzimage files - one with PAE enabled and one without. Anyway here's a good link to PAE & linux: http://www.spack.org/wiki/LinuxRamLimits
May 9, 200818 yr Author More links http://kerneltrap.org/node/2450 http://en.wikipedia.org/wiki/Physical_Address_Extension I think you might want to have two bzimages selectable from the syslinux menu. This may cut down on support. From what I was able to gather, PAE is enabled by a bit set in the CPU. I can only surmise that the kernel will still be in PAE mode if there is less then 4G of ram. I'll have to take out some ram and see what happens. From what I read any CPU from Pentium PRO and up should support PAE, so it may not be an issue. However, Theres a reason Red hat and the larger distro's create a hugemem kernel.
May 11, 200818 yr Author PAE mode works with 2GB. Can't quite tell if PAE mode is ignored if there is less then 4G, but at least the kernel works. I captured various syslogs in case someone wants to look at them real close.
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