Please help with a special RAID 1 setup

Hello all,
First excuse me for a looong message, but I've tryed to give as much
relevant details as possible.

Please help me with this weird setup if it is possible and fesable:

I have this raid1 device, composed of two fibre channel devices
mounted in RAID1, it works absolutely flawlessly.
The resulted device is used for a lot of important data logging and the ideea is to hotattach a 3-rd device ot the same size, wait for syncronisation and after all of them are syncronised, stop the data logging process, wait for a while, issue a sync command and hot detach the 3-rd device restart de data logging and walk away with valid filesytem backup of the main arry to be used as separate data analysys source. I know that solution is somewhat cumberome but trust me this is needed as is.
Now if you read untill here I managed to hot-attach, the attaching
was mentioned in the syslogfile, the data logging process continued undisturbed, even the cat /proc/mdstat showed the new device added BUT it only showed the same two [2/2] [UU] and it didn't touch the 3-rd disk at all, also hotremoving was sucessful.

Here are some relevant data of the test setup that may be usefull:

[root@test]# cat /etc/raidtab
raiddev /dev/md0
raid-level      1
nr-raid-disks   2
nr-spare-disks  0
chunk-size     4
persistent-superblock 1
device          /dev/sda2
raid-disk       0
device          /dev/sdb2
raid-disk       1

/proc/mdstat BEFORE adding the 3-rd device:

[root@test]# cat /proc/mdstat
Personalities : [raid1]
read_ahead 1024 sectors
md0 : active raid1 scsi/host3/bus0/target0/lun0/part2[1] scsi/host2/bus0/target0/lun0/part2[0]
     710938560 blocks [2/2] [UU]

unused devices: <none>

Then I add the 3-rd device:

[root@test]# raidhotadd /dev/md0 /dev/sdb3

/proc/mdstat AFTER adding 3-rd device

[root@nfs10 root]# cat /proc/mdstat
Personalities : [raid1]
read_ahead 1024 sectors
md0 : active raid1 scsi/host3/bus0/target0/lun0/part3[2] scsi/host3/bus0/target0/lun0/part2[1] scsi/host2/bus0/target0/lun0/part2[0]

     710938560 blocks [2/2] [UU]

unused devices: <none>

Piece of the syslog showing the add results:
.....

Jan  7 12:09:01 nfs10 kernel: md: updating md0 RAID superblock on device
Jan  7 12:09:01 nfs10 kernel: md: scsi/host3/bus0/target0/lun0/part3 [events: 00000012]<6>(write) scsi/host3/bus0/target0/lun0/part3's sb offset: 725598144
Jan  7 12:09:01 nfs10 kernel: md: scsi/host3/bus0/target0/lun0/part2 [events: 00000012]<6>(write) scsi/host3/bus0/target0/lun0/part2's sb offset: 710938560
Jan  7 12:09:01 nfs10 kernel: md: scsi/host2/bus0/target0/lun0/part2 [events: 00000012]<6>(write) scsi/host2/bus0/target0/lun0/part2's sb offset: 710938560

......

The problem is that no sync is done, as a matter of fact the 3rd
disk is not even scrached visibly ;(, did I miss someting obvious or what I want is impossible ???

Thank you for reading such a long mail and for any help that will
lead me solving this,

Mircea Ciocan

I think that you must replace:
nr-raid-disks 2
with
nr-raid-disks 3
Plus, the correspinding entry:
device /dev/sdb3
raid-disk 2

Else, the third drive isn't recognized as part of the md array. Probably, you must restart the array (only first time). You may want to use mdadm instead of raidtools.

---
Catalin(ux) BOIE
[email protected]

Modified config file, umounted and stoped raid, restarted raid,
hotadded the disk, still the same results :(.
Any other ideeas ??

Mircea

Can you give us the logs?

---
Catalin(ux) BOIE
[email protected]

I think you must rebuid the /dec/md0 with mkraid --upgrade. Warning! You may destroy all data, so backup first.

---
Catalin(ux) BOIE
[email protected]