[CentOS] Strange behavior from software RAID

Gerry Reno greno at verizon.net
Sun Mar 3 17:32:43 UTC 2013


You can usually generate a new mdadm.conf using:

rm /etc/mdadm.conf
mdadm --detail --scan >> /etc/mdadm.conf


On 03/02/2013 09:35 PM, Harold Pritchett wrote:
> Somewhere, mdadm is cacheing information.  Here is my /etc/mdadm.conf file:
>
> more /etc/mdadm.conf
> # mdadm.conf written out by anaconda
> DEVICE partitions
> MAILADDR root
> ARRAY /dev/md0 level=raid1 num-devices=4 metadata=0.90 UUID=55ff58b2:0abb5bad:42911890:5950dfce
> ARRAY /dev/md1 level=raid1 num-devices=2 metadata=0.90 UUID=315eaf5c:776c85bd:5fa8189c:68a99382
> ARRAY /dev/md2 level=raid1 num-devices=2 metadata=0.90 UUID=5b017f95:b7e266cc:f17a7611:8b752a02
> ARRAY /dev/md3 level=raid1 num-devices=2 metadata=0.90 UUID=4cc310ee:60201e16:c7017bd4:9feea350
> ARRAY /dev/md4 level=raid1 num-devices=2 metadata=0.90 UUID=ea205046:3c6e78c6:ab84faa4:0da53c7c
>
> After a system re-boot, here is the contents of /proc/mdstat
>
> # cat /proc/mdstat
> Personalities : [raid1]
> md125 : active raid1 sdc3[0]
>        455482816 blocks [2/1] [U_]
>
> md0 : active raid1 sdd1[3] sdc1[0] sdb1[1] sda1[2]
>        1000320 blocks [4/4] [UUUU]
>
> md127 : active raid1 sdd3[1] sdb3[0]
>        971747648 blocks [2/2] [UU]
>
> md3 : active raid1 sdf1[1] sde1[0]
>        1003904 blocks [2/2] [UU]
>
> md4 : active raid1 sdf3[1] sde3[0]
>        1948491648 blocks [2/2] [UU]
>
> md1 : active raid1 sda3[1]
>        455482816 blocks [2/1] [_U]
>
> unused devices: <none>
>
> There are six physical disks in this system:
>
> Disk /dev/sda:  500.1 GB, 500107862016 bytes
> Disk /dev/sdb: 1000.2 GB, 1000204886016 bytes
> Disk /dev/sdc:  500.1 GB, 500107862016 bytes
> Disk /dev/sdd: 1000.2 GB, 1000204886016 bytes
> Disk /dev/sde: 2000.3 GB, 2000398934016 bytes
> Disk /dev/sdf: 2000.3 GB, 2000398934016 bytes
>
> I used mdadm --examine /dev/sda1 to find the internal UUID for each of the physical volumes making up these volume groups
>
> /dev/sda1:  Magic : a92b4efc  Version : 0.90.00  UUID : 55ff58b2:0abb5bad:42911890:5950dfce
> /dev/sdb1:  Magic : a92b4efc  Version : 0.90.00  UUID : 55ff58b2:0abb5bad:42911890:5950dfce
> /dev/sdc1:  Magic : a92b4efc  Version : 0.90.00  UUID : 55ff58b2:0abb5bad:42911890:5950dfce
> /dev/sdd1:  Magic : a92b4efc  Version : 0.90.00  UUID : 55ff58b2:0abb5bad:42911890:5950dfce
> /dev/sda3:  Magic : a92b4efc  Version : 0.90.00  UUID : 315eaf5c:776c85bd:5fa8189c:68a99382
> /dev/sdc3:  Magic : a92b4efc  Version : 0.90.00  UUID : 315eaf5c:776c85bd:5fa8189c:68a99382
> /dev/sdb3:  Magic : a92b4efc  Version : 0.90.00  UUID : 5b017f95:b7e266cc:f17a7611:8b752a02
> /dev/sdd3:  Magic : a92b4efc  Version : 0.90.00  UUID : 5b017f95:b7e266cc:f17a7611:8b752a02
> /dev/sde1:  Magic : a92b4efc  Version : 0.90.00  UUID : 4cc310ee:60201e16:c7017bd4:9feea350
> /dev/sdf1:  Magic : a92b4efc  Version : 0.90.00  UUID : 4cc310ee:60201e16:c7017bd4:9feea350
> /dev/sde3:  Magic : a92b4efc  Version : 0.90.00  UUID : ea205046:3c6e78c6:ab84faa4:0da53c7c
> /dev/sdf3:  Magic : a92b4efc  Version : 0.90.00  UUID : ea205046:3c6e78c6:ab84faa4:0da53c7c
>
> As you can see, the UUID on the various PVs match the values in the /etc/mdadm.conf file.
>
> My question is What the heck is going on.  When I boot the system, I end up with two unexpected, unconfigured volume groups.  Where the heck are /dev/md125 and /dev/md127 coming 
> from?  They don't appear in /etc/mdadm.conf and if I re-boot they keep coming back.  It appears that somewhere mdadm is keeping information.  How can I get rid of it so the 
> mdadm.conf file is used.
>
> Harold
>
>
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