Re: How to Boot with LVM
Rick,
Thank you for responding and providing all the info.
On Monday, September 7, 2015 at 6:20:07 AM UTC-5, Rick Thomas wrote:
> On Sep 5, 2015, at 7:24 PM, ray wrote:
>
> > I would like to configure LVMs for everything including boot.
>
> Is it "just for fun" or do you have a real-world reason for wanting everything, including boot, to be on LVM?
Lack of knowledge. I was expecting it to be cleaner. But it no longer looks that way.
>
> I'll describe my own typical setup (special purpose systems may have different setups to meet special purpose needs). For purposes of illustration, I'll describe a system with two identical disks. The principles should be clear as they apply to systems with larger or more varied configurations. If you have only a single disk, you can skip the RAID parts in this and go straight to LVM.
I have 3 pairs of SSDs, each pair in a RAID0.
>
> I configure a small (<1GB) "/boot" partition as a primary partition (e.g. /dev/sda1) on one of the disks, with the same space on the other disk unused. [1] I make another primary partition (e.g. /dev/sd[ab]2) , on each of the disks, sized to be one half of the size I want for my swap. The rest of the space on each disk goes into a single, large, logical partition (e.g. /dev/sd[ab]5).
>
This is similar to my setup. I have the swaps on a separate RAID0.
> The two swap partitions I set up as a RAID0 (e.g. /dev/md0). This will be my system swap. [2]
>
> The two large logical partitions, I configure into a RAID1 (e.g. /dev/md1). [3]
>
I made my large partition a primary. Could this be problematic?
> I configure the RAID1 as the physical volume for a single volume group which I partition using LVM into a root that's big enough to be about 50% full when fully installed, and /home that's as big as I think I'll need for my users. The remainder of the VG I leave unconfigured, so I can grow into it as needs become apparent over time.
>
> If I have enough RAM to make it useful, I'll put /tmp on a tmpfs. I size it at about 50% of my swap space. With a smaller RAM, I make a separate logical volume for /tmp.
>
I would like to know more about the purpose of these criteria - please.
> [1] I know there are ways to make grub work with RAID1, but it's too complicated for me to get it right. Instead, I just make regular backups of the /boot partition. If the disk with /boot on it develops a bad spot in an inconvenient place, I simply boot from a CD in rescue mode and restore the contents of /boot from a backup into the unused space that I reserved on the other disk.
Yes, that was my plan also. But it was also my plan to backup the rest of the system to HDD. As such, I planned for no redundancy in drive configuration and only stripe for speed.
>
> [2] There's no particular point in putting swap on a redundant RAID. If your swap develops a bad spot, you probably want to boot from a CD into rescue mode ASAP so you can take necessary measures to fix the problem. Using RAID1 for swap would just mask the problem -- possibly until it's too late.
>
> [3] Conversely, everything else on the system wants to be redundantly protected. If I have three or more disks, I'll use RAID5; with four or more I might opt for RAID6.
>
> Here's an example:
>
> rbthomas@monk:~$ lsblk
> NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
> sda 8:0 0 465.8G 0 disk
> |-sda1 8:1 0 953M 0 part /boot
> |-sda2 8:2 0 18.6G 0 part
> | `-md0 9:0 0 37.3G 0 raid0 [SWAP]
> |-sda3 8:3 0 1K 0 part
> `-sda5 8:5 0 446.2G 0 part
> `-md1 9:1 0 446.1G 0 raid1
> |-root-root 253:0 0 18.6G 0 lvm /
> `-root-home 253:3 0 210G 0 lvm /home
> sdb 8:16 0 465.8G 0 disk
> |-sdb1 8:17 0 953M 0 part
> |-sdb2 8:18 0 18.6G 0 part
> | `-md0 9:0 0 37.3G 0 raid0 [SWAP]
> |-sdb3 8:19 0 1K 0 part
> `-sdb5 8:21 0 446.2G 0 part
> `-md1 9:1 0 446.1G 0 raid1
> |-root-root 253:0 0 18.6G 0 lvm /
> `-root-home 253:3 0 210G 0 lvm /home
> sr0 11:0 1 1024M 0 rom
>
>
> Enjoy!
> Rick
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