# Software RAID **URL:** \ **Category:** Filesystems, Disks and Memory\ **Created:** [December 7, 2009, 2:14pm UTC](https://community.unix.com/t/software-raid/255336 "2009-12-07T14:14:53Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![mojoman](https://community.unix.com/letter_avatar/mojoman/32/6_449c533f586939b6e5f246632a46421f.png) [@mojoman](https://community.unix.com/u/mojoman)\ **Post date:** [December 7, 2009, 2:14pm UTC](https://community.unix.com/t/software-raid/255336/1 "2009-12-07T14:14:53Z")
Hello, My company has inherited a Centos based machine that has 7 hard drives and a software based raid system. Supposedly one of the drives has failed. I need to replace the hardrive. How can I about telling which hard drive needs replacing? I have looked in the logs and there clearly is a problem there is no way I can tell which physical drive seems to have a problem. Advice? ---
**Author:** ![pludi](https://community.unix.com/user_avatar/community.unix.com/pludi/32/1278_2.png) [@pludi](https://community.unix.com/u/pludi)\ **Post date:** [December 7, 2009, 2:45pm UTC](https://community.unix.com/t/software-raid/255336/2 "2009-12-07T14:45:05Z")
Linux software RAID is usually managed through the mdadm tool. To see the status of the drives enter (replace /dev/md0 with the path to your actual RAID) ```nohighlight mdadm --detail /dev/md0 ``` ---
**Author:** ![mojoman](https://community.unix.com/letter_avatar/mojoman/32/6_449c533f586939b6e5f246632a46421f.png) [@mojoman](https://community.unix.com/u/mojoman)\ **Post date:** [December 7, 2009, 2:48pm UTC](https://community.unix.com/t/software-raid/255336/3 "2009-12-07T14:48:22Z")
How do I find out the path to the actual raid? Al I see is this: ```nohighlight [root@drill proc]# df Filesystem 1K-blocks Used Available Use% Mounted on /dev/mapper/VolGroup00-LogVol00 16790968 2805884 13118372 18% / /dev/hda1 101086 17720 78147 19% /boot tmpfs 777728 0 777728 0% /dev/shm /dev/md0 475751440 389860552 61724084 87% /ha0 ``` When I execute your command I get: ```nohighlight [root@drill proc]# mdadm --detail /dev/ha0 mdadm: cannot open /dev/ha0: No such file or directory [root@drill proc]# mdadm --detail /dev/md0 /dev/md0: Version : 00.90.03 Creation Time : Thu Mar 26 19:20:00 2009 Raid Level : raid1 Array Size : 483336128 (460.95 GiB 494.94 GB) Used Dev Size : 483336128 (460.95 GiB 494.94 GB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 0 Persistence : Superblock is persistent Update Time : Sun Dec 6 04:07:03 2009 State : clean Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0 UUID : 4a9f08c9:339514a7:b9ef28ff:12bbcfdb Events : 0.6 Number Major Minor RaidDevice State 0 253 2 0 active sync /dev/VolGroup_a/Logical_a 1 253 3 1 active sync /dev/VolGroup_b/Logical_b ``` ---
**Author:** ![pludi](https://community.unix.com/user_avatar/community.unix.com/pludi/32/1278_2.png) [@pludi](https://community.unix.com/u/pludi)\ **Post date:** [December 7, 2009, 3:50pm UTC](https://community.unix.com/t/software-raid/255336/4 "2009-12-07T15:50:17Z")
> [@mojoman](#): > > ```plaintext > [root@drill proc]# mdadm --detail /dev/ha0 > mdadm: cannot open /dev/ha0: No such file or directory > [root@drill proc]# mdadm --detail /dev/md0 > /dev/md0: > Version : 00.90.03 > Creation Time : Thu Mar 26 19:20:00 2009 > Raid Level : raid1 > Array Size : 483336128 (460.95 GiB 494.94 GB) > Used Dev Size : 483336128 (460.95 GiB 494.94 GB) > Raid Devices : 2 > Total Devices : 2 > Preferred Minor : 0 > Persistence : Superblock is persistent > > Update Time : Sun Dec 6 04:07:03 2009 > State : clean > Active Devices : 2 > Working Devices : 2 > Failed Devices : 0 > Spare Devices : 0 > > UUID : 4a9f08c9:339514a7:b9ef28ff:12bbcfdb > Events : 0.6 > > Number Major Minor RaidDevice State > 0 253 2 0 active sync /dev/VolGroup_a/Logical_a > 1 253 3 1 active sync /dev/VolGroup_b/Logical_b > > ``` In your case, /dev/md0 is the software RAID device. It's a RAID1 without any errors, using 2 devices, neither of them degraded or with errors. But none of the 2 is a physical device, but they are logical devices inside LVM volume groups. Which physical devices belong to it you'll see by checking the output of vgdisplay. From my point of view, it's been set up exactly the wrong way around. If a device fails, you'll have to rescue the volume group and logical devices before you'll be able to rescue the RAID. Also, any data not in the RAID will probably be lost, or at least will have to be restored from backup. Usually, you create a RAID (in hard- or software), on top of which you create logical devices. That way, if a drive fails it's easy to replace, and the LVM won't even notice a part of it went missing for a while. ---
**Author:** ![mojoman](https://community.unix.com/letter_avatar/mojoman/32/6_449c533f586939b6e5f246632a46421f.png) [@mojoman](https://community.unix.com/u/mojoman)\ **Post date:** [December 7, 2009, 3:57pm UTC](https://community.unix.com/t/software-raid/255336/5 "2009-12-07T15:57:42Z")
I do not see which physical groups they belong to after I run vgdisplay: ```nohighlight --- Volume group --- VG Name VolGroup00 System ID Format lvm2 Metadata Areas 1 Metadata Sequence No 3 VG Access read/write VG Status resizable MAX LV 0 Cur LV 2 Open LV 2 Max PV 0 Cur PV 1 Act PV 1 VG Size 18.53 GB PE Size 32.00 MB Total PE 593 Alloc PE / Size 593 / 18.53 GB Free PE / Size 0 / 0 VG UUID w7Ta2Z-Dx90-jg8v-28ZS-XT2x-zal6-Z7q3r1 --- Volume group --- VG Name VolGroup_a System ID Format lvm2 Metadata Areas 3 Metadata Sequence No 6 VG Access read/write VG Status resizable MAX LV 256 Cur LV 1 Open LV 1 Max PV 256 Cur PV 3 Act PV 3 VG Size 460.95 GB PE Size 4.00 MB Total PE 118004 Alloc PE / Size 118004 / 460.95 GB Free PE / Size 0 / 0 VG UUID ql9Zv1-wqXJ-4lPb-mmsM-lyaf-Bj10-rJGU1s --- Volume group --- VG Name VolGroup_b System ID Format lvm2 Metadata Areas 3 Metadata Sequence No 6 VG Access read/write VG Status resizable MAX LV 256 Cur LV 1 Open LV 1 Max PV 256 Cur PV 3 Act PV 3 VG Size 460.95 GB PE Size 4.00 MB Total PE 118002 Alloc PE / Size 118002 / 460.95 GB Free PE / Size 0 / 0 VG UUID RcIQpm-krvC-i3LD-eDQs-00Zy-mHoj-KChH9D ``` ---
**Author:** ![pludi](https://community.unix.com/user_avatar/community.unix.com/pludi/32/1278_2.png) [@pludi](https://community.unix.com/u/pludi)\ **Post date:** [December 7, 2009, 5:42pm UTC](https://community.unix.com/t/software-raid/255336/6 "2009-12-07T17:42:28Z")
You can get more details about a volume group using ```nohighlight vgdisplay VolGroup_a vgdisplay VolGroup_b ```