On 30/06/2011 11:51, Karsten Römke wrote:
Hello, I'm searching some hours / minutes to create a raid5 device with 4 disks and 1 spare: I tried first with the opensuse tool but no success as I want, so I tried mdadm Try: mdadm --create /dev/md0 --level=5 --raid-devices=4 --spare-devices=1 /dev/sda3 /dev/sdb2 /dev/sdc5 /dev/sdd5 /dev/sde5 leads to Personalities : [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] md0 : active (auto-read-only) raid5 sdd5[5](S) sde5[4](S) sdc5[2] sdb2[1] sda3[0] 13759296 blocks level 5, 64k chunk, algorithm 2 [4/3] [UUU_] 2 spares - I don't understand that. kspace9:~ # mdadm --create /dev/md0 --level=5 --raid-devices=4 /dev/sda3 /dev/sdb2 /dev/sdc5 /dev/sdd5 leads to md0 : active (auto-read-only) raid5 sdd5[4](S) sdc5[2] sdb2[1] sda3[0] 13759296 blocks level 5, 64k chunk, algorithm 2 [4/3] [UUU_] 1 spare - but why - I expect 4 active disks and 1 spare kspace9:~ # mdadm --create /dev/md0 --level=5 --raid-devices=5 /dev/sda3 /dev/sdb2 /dev/sdc5 /dev/sdd5 /dev/sde5 leads to md0 : active (auto-read-only) raid5 sde5[5](S) sdd5[3] sdc5[2] sdb2[1] sda3[0] 18345728 blocks level 5, 64k chunk, algorithm 2 [5/4] [UUUU_] That's what I want, but I reached it more or less by random. Where is my "think-error" (in german). I use kspace9:~ # mdadm --version mdadm - v3.0.3 - 22nd October 2009 Any hints would be nice
When you create a RAID 5 array, it starts degraded, and a resync is performed from the first N-1 drives to the last one. If you create a 5-drive RAID-5, this shows up as 4 drives and a spare, but once the resync is finished it's 5 active drives. Going back to your first attempt, it'll show as 3 drives and 2 spares, but once the initial resync is finished, it'll be 4 drives and 1 spare.
mdadm --detail /dev/md0 will show more information to confirm that this is what is happening.
Hope this helps. Cheers, John. -- 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
