As you may know I built a new file server, so the logical next step is to copy over the data from the old server. I did a simple rsync but soon realized that copying 214GB over the old server’s meager 100Mbps NIC was going to be painful. Not sure why but it was going very slow. Started the copy around lunch and by 5pm it had only done 30GB.
What can I do? Oh I can take out one of the drives from the old server and put it into the new one. Wait it’s a RAID drive. hrm. But it’s a RAID1 so I can use just one of the drives as a RAID device in degraded mode. This will surely work.
So I put the drive in the new machine. Next problem was how do I get the RAID drive as a new /dev/md2 device so I can mount the LVM partition from it to do the copy. WORDS OF CAUTION: if you do not know how to use mdadm read up on it BEFORE you attempt to mess around with it 
I proceeded to try out mdadm –create /dev/md2 –raid-devices=1 /dev/sde1 –force. This is NOT what you want to do if you want to keep the data on that drive 
No amount of lvm commands would help, which is obvious since I wiped it out. Ok now what?
I put the drive back into the old server, and since it was a RAID1, I can rebuild it. I first add the drive back to the RAID array:
# mdadm --manage /dev/md1 --add /dev/sdb1
# cat /proc/mdstat
md1 : active raid1 sda1[0] sdb1[1]
24418688 blocks [2/1] [U_]
[=>...................] recovery = 6.4%
I let that rebuild overnight. The next morning I move the drive back to the new server for yet another attempt at copying over the data. This time I am armed with more information.
First let’s see which drive it is:
# fdisk -l ... Disk /dev/sde: 250.1 GB, 250059350016 bytes 255 heads, 63 sectors/track, 30401 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00075dc6 Device Boot Start End Blocks Id System /dev/sde1 * 1 30401 244196001 fd Linux raid autodetect ...
Let’s scan the drive:
# mdadm --examine --scan /dev/sde1 ARRAY /dev/md2 UUID=061bae16:75f0a757:29aadef0:45edc6c0
I added the above to the bottom of /etc/mdadm.conf.
ARRAY /dev/md2 UUID=061bae16:75f0a757:29aadef0:45edc6c0 devices=/dev/sde1,missing
Then I restarted the array:
# mdadm -A -s
# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4] [raid1]
md2 : active raid1 sde1[1]
244195904 blocks [2/1] [_U]
md0 : active raid5 sdd1[3] sdb1[0] sdc1[1]
1953518592 blocks super 1.1 level 5, 512k chunk, algorithm 2 [3/3] [UUU]
bitmap: 2/8 pages [8KB], 65536KB chunk
unused devices:
Whew done. Wait no I’m not. I still need to mount the LVM volumes. Thankfully I didn’t
use the default of VolGroup00 (the default is now vg-machinename) on either of my machines. I used vol1 on the old machine and vg(0,1) on the new one. No conflicts to deal with. A quick
# vgchange -a y # mkdir /mnt/oldvol # mount /dev/vol1/lvvol /mnt/oldvol
Let’s check it:
# ls /mnt/oldvol/ backups lost+found music
# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg1-lvroot
70G 2.9G 64G 5% /
tmpfs 877M 0 877M 0% /dev/shm
/dev/sda1 485M 28M 432M 7% /boot
/dev/mapper/vg2-lvvol
1.8T 48G 1.7T 3% /vol
/dev/mapper/vol1-lvvol
226G 214G 641M 100% /mnt/oldvol
YAY! Now we can start copying data over the SATA bus which is rated at 3Gbps vs the NIC at 100Mbps.
Remember kids, if you don’t know how to use mdadm TREAD CAREFULLY!
