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Zucca
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 Posted: Fri May 26, 2023 4:07 pm Post subject: How far does GRUB capability with LVM (device-mapper) go? |
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As many of you know there's a lot of different layers to lvm.
GRUB advertises a capability to load kernel from lvm, but does it work if I have created /boot by | Code: | | lvcreate --type raid5 -i 3 --size <size> -n <lv_name> vg |
... for example?
If it can't I need to put kernel and initrd into EFI partition. Otherwise I can have a separate /boot formatted with XFS and all the reflinking goodness. ;)
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grknight
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Joined: 20 Feb 2015
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| Posted: Fri May 26, 2023 5:07 pm Post subject: |
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GRUB repository seems to indicate that LVM raid 1/4/5/6 are considered (as early as January 2012)
I have no idea if or how well it works. Would suggest light testing in a VM before applying to a real instance/machine. |
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Zucca
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| Posted: Fri May 26, 2023 6:36 pm Post subject: Thanks |
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grknight, thanks for the fast reply.
I guess I need to install qemu then.
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szatox
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| Posted: Fri May 26, 2023 7:28 pm Post subject: |
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| Quote: | If it can't I need to put kernel and initrd into EFI partition. Otherwise I can have a separate /boot formatted with XFS and all the reflinking goodness.  |
I think GRUB has full support for LVM, but there is little reason to use it on top of EFI:
There's nothing wrong with putting fat on boot partition and then not having a separate partition for /boot/efi. Also, refind is very simple to setup and does not require any maintenance at all. It just discovers all your kernels at boot time, and picks the one with the latest mtime. Press F2 for other options, touch an older kernel to make it default again.
No tricks with names or symlinks required, no need to regenerate configs etc. Just fire and forget, like a good loader should.
BTW, depending on how smart your mobo's efi is, you may find refind to be redundant too, and just boot directly instead. Refind is optional, but it would provide flexibility you might need once a blue moon, and shield you from bad EFI implementations. |
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Zucca
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| Posted: Fri May 26, 2023 8:08 pm Post subject: |
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szatox,
I use refind on almost all of my systems. And I really don't like autogenerating grub configs, in fact it completely missed my custom initrd while refind found it. And also on my usual setups my /boot is on fat.
But grub has more features and I've been planning to create much more simple grub script (config) by hand. I just need to get more familiar with it.
With scripting I can customize grub as much as I like. Debatable if I really need more customization for EFI/bootloader... But hey, this is Gentoo. ;)
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GDH-gentoo
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Joined: 20 Jul 2019
Posts: 1549
Location: South America
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| Posted: Fri May 26, 2023 8:58 pm Post subject: |
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| grknight wrote: | GRUB repository seems to indicate that LVM raid 1/4/5/6 are considered (as early as January 2012)
I have no idea if or how well it works. |
sys-boot/grub-2.06-r6 seems to be able to read from LVs of type raid5 for me, so I suppose it should be able to boot from them, too:
On Gentoo:
| Code: | # lvs -o name,lv_layout vg_test
LV Layout
RaidTest raid,raid5,raid5_ls |
On GRUB, after dropping to the CLI from the menu with c:
| Code: | grub> insmod lvm
grub> ls (lvm/vg_test-RaidTest)/
lost+found/ dir1/ dir2/
grub> ls (lvm/vg_test-RaidTest)/dir1
file1
grub> cat (lvm/vg_test-RaidTest)/dir1/file1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 |
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szatox
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| Posted: Fri May 26, 2023 10:51 pm Post subject: |
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| Zucca wrote: | szatox,
[..]
With scripting I can customize grub as much as I like. Debatable if I really need more customization for EFI/bootloader... But hey, this is Gentoo. |
I see. Well, I'm not one to take your hobby from you.
However, it does sound so absurd you actually got me curious now. What are you trying to do there? |
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Zucca
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Location: Rasi, Finland
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| Posted: Sat May 27, 2023 6:13 am Post subject: |
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| szatox wrote: | | However, it does sound so absurd you actually got me curious now. What are you trying to do there? |
My long time plan has been to simplify grub configuration creation (since grub2 was released, I've been using refind because in my eyes grub config creation is a big mess). Make one static config (script) that resides on EFI partition. Optionally (probably required) is another config file which contains settings like | Code: | root=UUID=BEEF
rootfsflags=ro,noatime |
which is then sourced by the main grub config. The settings file would be the single and only file to be edited (or automatically generated).
I hope that this kind of setup is possible.
The grub lvm support is just another nice-to-have feature, not really related to my plans.
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szatox
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| Posted: Sat May 27, 2023 8:58 am Post subject: |
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So, basically you want to make grub operate like refind with extra steps.
Well, it should be doable, grub does support includes and variables, so probably not even that difficult to configure, but at the same it might to be quite fragile, since you'd be doing that thing called "not-what-the-authors-expected".
Do you have any particular use case that needs such custom setup, or doing this just for fun and challenge?
Or maybe you made a bet or something?  |
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Zucca
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| Posted: Sat May 27, 2023 3:58 pm Post subject: |
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Well. There's the "learning to grub" -part and with that I could make some my custom usb live sticks.
But mostly because I have always thought that creating complex script with a bunch of scripts is somewhat mad.
"There's got to be a simpler way" is what drove me to this.
Normally I'd use refind... and I do. It's far simpler and better with "normal setups" than grub.
I also wrote my own initrd creation tool... so yeah.
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