we have a number of systems that have a large number of software arrays running. its in the couple hundred range. we have been using a custom built kernel based on 3.4 but are wanting to update to a mainline kernel and have been experimenting with 4.4. the systems are running recent centos 6 releases but we have been downgrading the mdadm version from 3.3.2 in 6.7 to a custom build 3.2.6. we installed the downgraded version due to a problem with array numbering. i emailed the list a while ago explaining the issue and submitting a patch to fix [1]. i never heard anything back and since we had a simple fix i didn't follow up on it. unfortunately, when testing the 3.2.6 mdadm with linux kernel 4.4 wasn't working. mdadm and the kernel would complain about the devices not having a valid v1.2 superblock and not start the array. testing with 3.3.2 from the current centos repos worked. i'd like to update but we still have the issue with lots of arrays mentioned previously. i spent some time checking to make sure that my patch rebases against master properly (and it does) but during testing i was unable to create an array with number larger than /dev/md511 when using the 4.4 kernel we were testing as well as the 4.2 kernel i had on another test box. creating one larger than 511 on a system with a 3.16 kernel worked. it looks like something broke between kernel 3.16 and 4.2 that limited the number of arrays to 512 (/dev/md0 to /dev/md511). this was a problem regardless of mdadm version and i haven't yet done much digging into the problem. there are a couple things that could potentially be done. the easiest, would be to just modify find_free_devnm() in mdopen.c from wrapping to (1<<20)-1 and instead have it wrap around to (1<<9))-1. this would limit mdadm to 512 auto-generated array numbers. i'm guessing this would be sufficient for the vast majority of cases and would solve the problem i'm facing at work. the next option would be to apply the patch in my previous email and then figuring out why the newer versions of the kernel don't support more than 512 arrays. this would take more work but probably the better long term approach. what do you all think? thanks mike [1] http://marc.info/?l=linux-raid&m=142387809409798&w=2 -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
