[arch-general] mkinitcpio: mdadm_udev Hook
Hi, I've just been re-installing a box, and saw that the wiki says regarding using the mdadm_udev hook:
"This is the preferred method of mdadm assembly (rather than using the above mdadm hook). "
I've tried to use the mdadm_udev hook, but the devices get named:
normal md0 (/boot) is md127 normal md1 (encrypted, then lvm with swap and / on it ) is md126
I found this out with "cat /proc/partitions" once my box failed to boot and dropped to the initramfs shell. Seems pretty random, the first actual device isn't even the lowest number. There doesn't seem to be any documented way to have my raid1 devices named so I can use:
cryptdevice=/dev/md1:crypt
in my kernel arg line. The only way to get things to work is to use the mdadm hook and have my devices specified in /etc/mdadm.conf Can I rely on md127 and md126 being the same across every boot, and therefore resign myself to using this numbering (instead of the much nicer md0 and md1), and use it in my cryptdevice kernel arg and be done with it? Given this thread: https://bbs.archlinux.org/viewtopic.php?id=149358 And the comment: "I have little interest in supporting the mdadm hook. Assembly via udev is the preferred method here." What is the right way to do this? Cheers. -- Simon Perry (aka Pezz)
Am 03.10.2012 14:41, schrieb Simon Perry:
Hi,
I've just been re-installing a box, and saw that the wiki says regarding using the mdadm_udev hook:
"This is the preferred method of mdadm assembly (rather than using the above mdadm hook). "
I've tried to use the mdadm_udev hook, but the devices get named:
normal md0 (/boot) is md127 normal md1 (encrypted, then lvm with swap and / on it ) is md126
I found this out with "cat /proc/partitions" once my box failed to boot and dropped to the initramfs shell.
Seems pretty random, the first actual device isn't even the lowest number.
You need to create a file /etc/mdadm.conf. mdadm --examine --scan will generate the right lines for you. This file will be added to the initramfs and your names will be fine again.
On 03/10/12, Thomas Bächler wrote: | You need to create a file /etc/mdadm.conf. mdadm --examine --scan will | generate the right lines for you. This file will be added to the | initramfs and your names will be fine again. Yep, that's what I've done, and I've used the mdadm hook as I have in the past. Based on the mkinitcpio wiki page, and the forum post, I'm under the impression that using mdadm_udev to auto-assemble the arrays is what I should be using (and is what will be supported in the future). The mdadm_udev hook does work as advertised, but I don't see how I can use it when I need a known /dev/mdx device for use in something like a "cryptdevice=" kernel arg. Cheers. -- Simon Perry (aka Pezz)
Am 03.10.2012 22:07, schrieb Simon Perry:
Based on the mkinitcpio wiki page, and the forum post, I'm under the impression that using mdadm_udev to auto-assemble the arrays is what I should be using (and is what will be supported in the future).
The mdadm_udev hook does work as advertised, but I don't see how I can use it when I need a known /dev/mdx device for use in something like a "cryptdevice=" kernel arg.
First of all, once you add the mdadm.conf file, the mdX names will follow the naming usual scheme - the md126+ names will only be used when the array is not mentioned in mdadm.conf. Second, you can always use /dev/disk/by-uuid/.
On 03/10/12, Thomas B?chler wrote:
You need to create a file /etc/mdadm.conf. mdadm --examine --scan will generate the right lines for you. This file will be added to the initramfs and your names will be fine again.
Yep, that's what I've done, and I've used the mdadm hook as I have in the past.
Based on the mkinitcpio wiki page, and the forum post, I'm under the impression that using mdadm_udev to auto-assemble the arrays is what I should be using (and is what will be supported in the future).
The mdadm_udev hook does work as advertised, but I don't see how I can use it when I need a known /dev/mdx device for use in something like a "cryptdevice=" kernel arg.
Thomas is pointing out that the mdadm_udev hook will (should?) still honor your /etc/mdadm.conf if it has ARRAY decls in it (you'll see it being picked up on the mkinitcpio run if this is true). If that isn't happening, or it isn't being honored, we should find out why. Alternatively, cryptdevice understands tags, e.g: cryptdevice=UUID=46c78135-8ac0-4928-8b26-5d23a77b1ff1:cryptrewt Of course, since there isn't a filesystem involved, UUID is the only one that makes sense for MBR disks. PARTUUID is also supported, and PARTLABEL support will be available in the next mkinitcpio release. Cheers, Dave
On 03/10/12, Thomas Bächler wrote: | First of all, once you add the mdadm.conf file, the mdX names will | follow the naming usual scheme - the md126+ names will only be used when | the array is not mentioned in mdadm.conf. | | Second, you can always use /dev/disk/by-uuid/. Cool, makes sense, and damn me for not going one step further and setting up mdadm.conf before giving up and going back to the mdadm hook. :) -> Running build hook: [mdadm_udev] Custom /etc/mdadm.conf file will be used in initramfs for assembling arrays. Cheers for the info fellas. -- Simon Perry (aka Pezz)
participants (3)
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Dave Reisner
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Simon Perry
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Thomas Bächler