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Phillip Susi wrote: > Did you direct the program to use O_DIRECT? I'm just using the s/w (iorate/bonnie++) with default options - I'm no expert. I could try though. > If not then I believe the > problem you are seeing is that the generic block layer is not performing > large enough readahead to keep all the disks in the array reading at > once, because the stripe width is rather large. What stripe factor did > you format the array using? I left the stripe size at the default, which, I believe, is 64K bytes; same as your fakeraid below. I did play with 'blockdev --setra' too. I noticed it was 256 with a single disk, and, with s/w raid, it increased by 256 for each extra disk in the array. IE for the raid 0 array with 4 drives, it was 1024. With h/w raid, however, it did not increase when I added disks. Should I use 'blockdev --setra 320' (ie 64 x 5 = 320, since we're now running RAID5 on 5 drives)? > I have a sata fakeraid at home of two drives using a stripe factor of 64 > KB. If I don't issue O_DIRECT IO requests of at least 128 KB ( the > stripe width ), then throughput drops significantly. If I issue > multiple async requests of smaller size that totals at least 128 KB, > throughput also remains high. If you only issue a single 32 KB request > at a time, then two requests must go to one drive and be completed > before the other drive gets any requests, so it remains idle a lot of > the time. I think that makes sense (which is a change in this RAID performance business :( ). Thanks. Max. > Max Waterman wrote: >> Hi, >> >> I've been referred to this list from the linux-raid list. >> >> I've been playing with a RAID system, trying to obtain best bandwidth >> from it. >> >> I've noticed that I consistently get better (read) numbers from kernel >> 2.6.8 >> than from later kernels. >> >> For example, I get 135MB/s on 2.6.8, but I typically get ~90MB/s on later >> kernels. >> >> I'm using this : >> >> <http://www.sharcnet.ca/~hahn/iorate.c> >> >> to measure the iorate. I'm using the debian distribution. The h/w is a >> MegaRAID >> 320-2. The array I'm measuring is a RAID0 of 4 Fujitsu Max3073NC >> 15Krpm drives. >> >> The later kernels I've been using are : >> >> 2.6.12-1-686-smp >> 2.6.14-2-686-smp >> 2.6.15-1-686-smp >> >> The kernel which gives us the best results is : >> >> 2.6.8-2-386 >> >> (note that it's not an smp kernel) >> >> I'm testing on an otherwise idle system. >> >> Any ideas to why this might be? Any other advice/help? >> >> Thanks! >> >> Max. >> - >> To unsubscribe from this list: send the line "unsubscribe >> linux-kernel" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> Please read the FAQ at http://www.tux.org/lkml/ >> >> > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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