[SOLVED] fakeRAID:0 install

quequotion · 2014-01-19 21:59:08

Ran into another hangup during install: I can't find a way to initialize my fakeRAID:0 array.

The specific problem I had appears to be known and left unresolved.

According to what speculation I could find, mdadm should support my ISW fakeRAID; in fact it appears to find the array (/dev/md/dm-0), but doesn't load any of the raid's partitions (there should be a fat32 efi partition, an ext4 root partiition, and a swap partition).

I'm not familiar with mdadm either, although I was able to find out it knows the correct name of the array from metadata (--examine --scan) "main" (unless it's a coincidence that it calls the array main and I named it main in UEFI)

I could try the older livecd (as recommened on the wiki and in the closed task ...for different reasons), if then updating to the latest arch packages will not render the raid unsuable.

I'd like to avoid any action that will render my computer unusable without confidence that I will be able to install arch.

::EDIT::

Wrong link for "known and left unresolved" issue with dmraid affecting all installation media after 2010.05

Last edited by quequotion (2014-02-15 03:38:43)

quequotion · 2014-01-20 04:03:33

One of the comments in the closed task has instructions for mdadm:

I reinstalled using mdadm, it works. In the 2012.01.25 iso, the mdadm partitions are not listed in the installer, but they are in 2012.01.26. Partitions are /dev/md128p?, they are presented right after ISO boot, there is nothing special to do.
You have to add your filesystem module manually in mkinitcpio.conf (e.g. ext4), as well as your raid module (e.g. raid0). I added /sbin/mdadm in the binairies for convenience, if ever I couldn't boot. Honestly, I had to reboot 4 times before figuring out how to configure it. I used syslinux as bootloader, because it is raid aware. Also, take care of the /etc/mdadm.conf. You have to generate it manually:
mdadm --examine --scan > /mnt/etc/mdadm.conf
before generating the initcpio. https://wiki.archlinux.org/index.php/RAID has good infos.
The problem is, during all my manipulations, I set the partition table to GPT, so my Windows don't boot anymore as GPT without UEFI is not supported.

It's hard to tell if this is about setting up an arch installation or installing from a cd. I don't know if it's possible to generate initcpio and reload it for a running operating system (on the installation cd).

Is there some way I could fix mdadm to load the partitions?

Also, although the task went unresolved and no one ever seems to have found the problem, there is this warning on the wiki:

Warning: Command "dmraid -ay" could fail after boot to Arch linux Release: 2011.08.19 as image file with initial ramdisk environment does not support dmraid. You could use an older Release: 2010.05. Note that you must correct your kernel name and initrd name in grubs menu.lst after installing as these releases use different naming

Is this the actual cause of the problem with dmraid on all installation media after 2010.05?

Last edited by quequotion (2014-01-20 04:05:42)

jasonwryan · 2014-01-20 04:27:27

I don't know anything about fake raid, but have used mdadm for years without any issues.

You can set it all up from the live environment; as the poster in the bug report notes, just make sure that you include the relevant modules in mkinitcpio.conf (and use the mdadm-udev hook).

quequotion · 2014-01-20 16:27:59

jasonwryan wrote:

I don't know anything about fake raid, but have used mdadm for years without any issues.
You can set it all up from the live environment; as the poster in the bug report notes, just make sure that you include the relevant modules in mkinitcpio.conf (and use the mdadm-udev hook).

Do you mean that it is possible to regenerate the initcpio from a running system and reload it into that very same system without rebooting?

This has to work strictly from the live cd, before installing any part of arch to disk (because there are no disks to install to without this), which means that it is not possible to do anything that involves a reboot.

::EDIT::

You can set it all up from the live environment

The problem is that I need it set up in the live environment.

Last edited by quequotion (2014-01-20 17:01:38)

quequotion · 2014-01-20 17:33:57

Could I use kernel parameters to load the modules I need?

quequotion · 2014-01-20 17:47:38

Or would mdadm be able to fully initialize the raid if I modprobe the appropriate modules? (ie raid0 and ...? )

jasonwryan · 2014-01-20 19:45:44

quequotion wrote:

jasonwryan wrote:
You can set it all up from the live environment
The problem is that I need it set up in the live environment.

Please read the wiki chroot article: that is exactly what you are doing when you install Arch.

quequotion · 2014-01-21 03:14:04

I don't mean to keep asking over and over but I am confused as to how this works.

I'm stuck at the install step "Prepare the storage drive". I have no arch installation to work with; there's nowhere to chroot into.

I'm not trying to install arch with raid support; I'm trying to install arch on a raid. I need to access partitions that exist on my array in the live environment before I can proceed.

How I expect this to work:

1. Boot from install cd (2014.01.50, requires "nomodeset" kernel option for nvidia gpu). OK
2. "Establish a network connection" (requires installation of "ifuse" and dependencies because I have only an ipheth connection). OK
3. "Prepare the storage device" (access fakeRAID:0's three partitions so they can be prepped for installation). fakeRAID:0 device file exists, but no devices exist for its partitions
4~?. Proceed with installation.

I can't find the raid partitions in the live environment. It seems mdadm should have automatically loaded the array, but it hasn't created device files for any of it's partitions. The only alternative, dmraid, isn't operational due to a known bug.

I suspect the live environment is not loading the necessary modules (raid0? dm_mod?). The instructions above specify that the necessary modules must be loaded by initcpio. How can I add anything to the live environment’s pre-compiled initcpio?

If it's possible to load the partitions manually with modprobe and mdadm (and udev?), I need instruction on how to do so (doing this in the live environment isn't specified in the wiki; the fakeRAID installation procedure outlines a dmraid method marked as out-of-date).

I imagine that might work like (and I'll give this a try later):

modprobe dm_mod
modprobe raid0
mdadm --assemble --scan

Unfortunately this is my first time working with both mdadm and arch, so I have no idea what is and isn't possible.

Last edited by quequotion (2014-01-21 03:30:55)

jasonwryan · 2014-01-21 04:08:02

OK: that is much clearer, I think I am with you now.

When you have a prompt in the live environment, you can `modprobe` any modules you need; you don't need to rebuild the initrd for the archiso (unless the modules you are looking for are particularly exotic and raid0 and dm-mod do not fall into that category).

Then, run `cat /proc/mdstat` to see if the arrays have been recognized and assembled. If they have not, use `mdadm --assemble /dev/md0 /dev/sd[ab]1` etc., to assemble them.

When you chroot into the running system, that's when you add the modules and hook the the intird conf).

quequotion · 2014-01-22 03:53:57

Issue resolved! Thanks for the advice!

Gdisk pointed out some issues with the partitions that Ububtu never seemed to care about. "One or more CRCs don't match, Repair the disk"; "Partition [1~3] does not start on an 8-somethingorother"; "Partition 3 is too big for this disk"; "Invalid something backup, regenerating"; "some other problem fixed by 'x' then 'e'". All of which were resolved by repartitioning the drive.

After repartitoning, I finally got devices for the parttions. These have persisted across several reboots into the live environment. From the looks of it, the fakeRAID support I was looking for has been there all along, but arch is more picky about what quality of partitions it will allow to become block devices compared to other distros.

That's probably a good thing, but maybe it should be noted in the wiki: sub-par partitions will be ignored.
Actually, the fakeRAID install wiki needs to be revamped anyway. If can get arch to connect to the internet and load a desktop within the week I might even make some adjustments myself.

jasonwryan · 2014-01-22 04:48:44

Good to know. Welcome to Arch!

Please remember to mark your thread as [Solved] by editing your first post and prepending it to the title.

Arch Linux

#1 2014-01-19 21:59:08

[SOLVED] fakeRAID:0 install

#2 2014-01-20 04:03:33

Re: [SOLVED] fakeRAID:0 install

#3 2014-01-20 04:27:27

Re: [SOLVED] fakeRAID:0 install

#4 2014-01-20 16:27:59

Re: [SOLVED] fakeRAID:0 install

#5 2014-01-20 17:33:57

Re: [SOLVED] fakeRAID:0 install

#6 2014-01-20 17:47:38

Re: [SOLVED] fakeRAID:0 install

#7 2014-01-20 19:45:44

Re: [SOLVED] fakeRAID:0 install

#8 2014-01-21 03:14:04

Re: [SOLVED] fakeRAID:0 install

#9 2014-01-21 04:08:02

Re: [SOLVED] fakeRAID:0 install

#10 2014-01-22 03:53:57

Re: [SOLVED] fakeRAID:0 install

#11 2014-01-22 04:48:44

Re: [SOLVED] fakeRAID:0 install

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