Good point. I didn't do that step, but I found when I reboot the machine it sorts everything out on its own anyway. For safety, it is probably better to include that step.
On 18-10-04 01:23 PM, Gilles Detillieux wrote:
Thanks, Scott.
One of the steps in the tutorial is to save the MD RAID configuration in /etc/mdadm/mdadm.conf. They suggest using "sudo mdadm --detail --scan | sudo tee -a /etc/mdadm/mdadm.conf", which I did. In your approach, that step isn't done. Is this a detail that pvcreate looks after for you, either by adding to that file itself, or saving the setup elsewhere? This was the only part of DigitalOcean's procedure that I found to be a bit kludgy. I was surprised that there wasn't something right in mdadm to manage the saving of the configuration more automatically. Adding the fstab entry was as I'd expect for any file system type. Other than that, things were pretty plug-and-play, with no messing around with systemctl or anything like that required. After a reboot, the RAID array was back in action just as it should be.
On 10/04/2018 10:07 AM, Scott Toderash wrote:
Here are my notes from the last time I build a Linux RAID on LVM. This was on 16.04LTS
I think my approach was slightly different. The RAID device is created on the LVM devices.
- create partitions of type Linux RAID Autodetect on both disks
fdisk -l /dev/sdb fdisk -l /dev/sdc 2. create a RAID array called md0 using mdstat sudo mdadm --create /dev/md0 --level=mirror --raid-devices=2 /dev/sdb1 /dev/sdc1 3. add the md0 raid device to the LVM pool sudo pvcreate /dev/md0 4. create a volume group called datavg sudo vgcreate datavg /dev/md0 5. create a logical volume called datalv within the volume group sudo lvcreate --name datalv --size 1.8T datavg 6. format the newly created logical volume sudo mkfs.ext4 /dev/datavg/datalv 7. move home files to a temporary location, create a new home and mount the newly formatted device there, copy the original home files to the new device sudo mv home home.orig; sudo mkdir home ; sudo chmod 777 home ; sudo mount /dev/mapper/datavg-datalv /home ; sudo cp -a /home.orig/* home 8. edit fstab for startup config for this disk
On 18-10-04 09:42 AM, Gilbert E. Detillieux wrote:
I think the tutorial is complete enough. The only thing I'd do differently is create appropriate partition tables on the raw disks (GPT if the disks are >2TB or if you need to use GPT for other reasons, but the older MS-DOS partition tables would be fine otherwise), set up one partition on each drive and tag them with the applicable partition type to indicate they're MD RAID partitions, and use the device names for the partitions rather than the raw drives in the mdadm commands. While this isn't necessary, I think it would help in post-mortem recovery, and in keeping your sanity when you're (or someone else is) trying to figure out what you did a few years later.
LVM has some nice features to offer, e.g. if you anticipate wanting to add more capacity to this file system in the future, or you want to split a large array into multiple file systems. But for simple use cases, I wouldn't bother. If you do use LVM, don't use its RAID features; use LVM over top of MD.
If you go with GPT partition format, and don't want to deal with the arcane syntax of parted commands, there are alternatives: gparted for the full-GUI, Partition-Magic-like experience, or gdisk for a simple fdisk-like, retro, text-menu-based interface.
Gilbert
On 04/10/2018 8:33 AM, Gilles Detillieux wrote:
Circumstances finally forced me to bite the bullet and learn something I had been putting off for too long: setting up a RAID array under Linux. I'm almost embarrassed, now that I've done it, that I waited so long because it was way simpler than I'd imagined. I thought I'd have to figure out all kinds of magic with LVM, parted, and mdadm, but I found this tutorial that showed a simple set of mdadm commands to set up RAID 1:
https://www.digitalocean.com/community/tutorials/how-to-create-raid-arrays-w...
This was actually one of the simplest scenarios: the system had an SSD for the root/boot partition, and two 2 TB hard drives for data storage (/dev/sdb & sdc), so I just needed to set up RAID 1 and not worry about the intricacies of booting from RAID. So, software RAID seemed like the quick & easy way to go with a minimum of fuss.
Now the nagging question: is it really this simple, or does the tutorial above oversimplify and omit some important steps? Can someone with ample RAID and mdadm experience advise or provide tips on anything else I should do or lookout for?
Thanks, Gilles