Hi All, Firstly, I must express my thanks to Neil Brown for being willing to respond to the direct email I sent him as I couldn't for the life of me find any forums on mdadm or this list... I have a Software RAID 5 device configured, but one of the drives failed. I removed the drive with the following command... mdadm /dev/md0 --remove /dev/hdc1 [root@space ~]# cat /proc/mdstat Personalities : [raid6] [raid5] [raid4] md1 : active raid5 hdk1[5] hdi1[3] hdh1[2] hdg1[1] hde1[0] 976590848 blocks level 5, 64k chunk, algorithm 2 [5/4] [UUUU_] [====>................] recovery = 22.1% (54175872/244147712) finish=3615.3min speed=872K/sec md0 : active raid5 sdd1[4] sdc1[2] sdb1[1] sda1[0] 1953535744 blocks level 5, 64k chunk, algorithm 2 [5/4] [UUU_U] unused devices: <none> Please ignore /dev/md1 for now at least. Now my array (/dev/md0) shows the following... [root@space ~]# mdadm -QD /dev/md0 /dev/md0: Version : 00.90.03 Creation Time : Wed Jan 9 18:57:53 2008 Raid Level : raid5 Array Size : 1953535744 (1863.04 GiB 2000.42 GB) Used Dev Size : 488383936 (465.76 GiB 500.11 GB) Raid Devices : 5 Total Devices : 4 Preferred Minor : 0 Persistence : Superblock is persistent Update Time : Tue Jan 4 04:28:03 2005 State : clean, degraded Active Devices : 4 Working Devices : 4 Failed Devices : 0 Spare Devices : 0 Layout : left-symmetric Chunk Size : 64K UUID : 382c157a:405e0640:c30f9e9e:888a5e63 Events : 0.337650 Number Major Minor RaidDevice State 0 8 1 0 active sync /dev/sda1 1 8 17 1 active sync /dev/sdb1 2 8 33 2 active sync /dev/sdc1 3 0 0 3 removed 4 8 49 4 active sync /dev/sdd1 Now, when I try to insert the replacement drive back in, I get the following... [root@space ~]# mdadm /dev/md0 --add /dev/hdc1 mdadm: add new device failed for /dev/hdc1 as 5: Invalid argument It seems to be that mdadm is trying to add the device as number 5 instead of replacing number 3, but I have no idea why, or how to make it replace number 3. --- Neil has explained to me already that the drive should be added as 5, and then switched to 3 after a a rebuild is complete. Neil aslo asked me if dmesg showed up anything when I tried adding the drive [root@space mdadm-2.6.4]# dmesg | tail ... md: hdc1 has invalid sb, not importing! md: md_import_device returned -22 md: hdc1 has invalid sb, not importing! md: md_import_device returned -22 I have updated mdadm to the latest version I can find... [root@space ~]# mdadm --version mdadm - v2.6.4 - 19th October 2007 Still get the same error. I'm hoping someone will have some suggestion as to how to sort this out. Backing up nearly 2TB of data isn't really a viable option for me, so I'm quite desperate to get the redundancy back. My linux distribution is a relatively new installation from CentOS 5.1 ISOs. The Kernel version is [root@space ~]# uname -a Linux space.homenet.com 2.6.18-53.1.4.el5 #1 SMP Fri Nov 30 00:45:55 EST 2007 x86_64 x86_64 x86_64 GNU/Linux Many Thanks, Steve. No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: 269.19.7/1232 - Release Date: 18/01/2008 19:32 - 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