NVRAID, LVM, dm-crpyt, selfcompiled kernel, initramfs

Baarn · n00b Joined: 02 Mar 2011 Posts: 17

Hey, I think the title tells what I want to do, but some advice so I won't forget anything.
I already read through those guides:
http://en.gentoo-wiki.com/wiki/RAID/NVRAID_with_dmraid
http://en.gentoo-wiki.com/wiki/Root_filesystem_over_LVM2,_DM-Crypt_and_RAID

ok, so my plan is simple:
I have a group of two 74GB drives and another group of two 2TB drives both mirrored with RAID1.
my partition table should look something like this:
on 74GB drives:
pri1 - /boot - unencrypted 100M
pri2 - dm-crypt-vg with lvm
- /root 15GB
- /swap 5GB
- /tmp 5GB
- /var 10GB
- /usr 100%left
/home wont get its own partition for now, it can stay under /root and i will move it to the 2TB drives when i have a running system.

so what i did till now:
i was able to find the raid-arrays and to partition them, in the next step i will build the complete cryptostuff on top.
my fear is remounting the partitions after reboot wont work, i have little to zero knowledge about init ramfs and i really don't know what to do here especially because the nvraid guide is from 2006.
are there any other guides, any recommendations? do i really need grub2?

(edit: i confused initscripts with initramfs ...)

Hu · Administrator Joined: 06 Mar 2007 Posts: 21706

Your choice of bootloader is independent of what kernel you run or what initramfs, if any, it uses. You can use Grub Legacy, Grub2, LILO, or Syslinux to load your kernel. Once your kernel is loaded, its initramfs will need to discover any software RAID volumes and unlock any required encrypted volumes. An optional encrypted volume would be something like /home or a private files area, which is not required to boot the system. The instructions in the LVM2 Wiki article are outdated and ask you to copy the initramfs files instead of using the kernel build system to create it. The sample init should work, but is also outdated. You can use a devtmpfs instead of a static dev in the initramfs, which avoids problems with device numbers becoming stale.

I believe the warning about Grub Legacy vs. Grub2 only applies if you intend to have /boot be on a software RAID partition. If you only RAID the main system, then you can use Grub Legacy.

NeddySeagoon · Posted: Sat Jul 23, 2011 6:14 pm Post subject:

Baarn,

nvraid is fakeraid - the only excuse for using fake raid is that windows must share the raid set.

Kernel raid is lower latency than nvraid. nvraid will only ever read from one drive in the mirror. kernel raid positions the heads of the drives in the mirror set over different tracks the reads from whichever drive has the head closest to the needed data.

Lastly, the data layout on the drives with fakeraid determined by your chipset and BIOS. If you ever need to move the raid drives to another motherboad, it needs the *identical* chipset and BIOS.
Kernel raid sets are hardware independent.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

Baarn · n00b Joined: 02 Mar 2011 Posts: 17

awww damn, i read in the guide that nvraid is slower than software raid, but some guy told me, that that was only the case for older chipsets.
is there an easy way to unsync the discs and apply software raid to them, or do i have to repartition (and install) everything?

@Hu
i only get half of what you're saying. whats the kernel build system? i mean i built some kernels, but never needed an initramfs, or is that always built into the kernel in some way?
and i think, after what NeddySeagoon said its better to use software-raid, which of course means that my /boot is on the software-raid as well.

can i just stick to this
http://en.gentoo-wiki.com/wiki/Root_filesystem_over_LVM2,_DM-Crypt_and_RAID
then and it will work?

Hu · Administrator Joined: 06 Mar 2007 Posts: 21706

Baarn · n00b Joined: 02 Mar 2011 Posts: 17

OK, thanks for the help

I think I try to go with Grub2 and do it the hard way. The main purpose of that computer is to get as much nasty stuff onto it as possible, if I wanted the easy way I could just install Ubuntu

At least i will learn something.

NeddySeagoon · Posted: Sat Jul 23, 2011 11:22 pm Post subject:

Baarn,

grub 1 works fine on software raid1. Its simply ignores the raid structure but ...
You must create the /boot raid set with version 0.90 metadata, or grub won't boot.

Fakeraid is another version of software raid. Its just not as mature or hardware independent as kernel raid.
The speed you get is down to the software, not the hardware.

IF you want to be first into the future, rather than last out of the past, use parted and GPT partition tables, not fdisk and MSDOS Partition tables.
Watch out for the 4k phyisical sectors on your 2T drives. Properly aligned partitions are essential.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

Baarn · n00b Joined: 02 Mar 2011 Posts: 17

my small drive is now allready partitioned with sfdisk (sounds like its fdisk too)
I think I will repartition with parted then

Are there any true downsides on using grub2? I never had problems with it on my Xubuntu laptop, so I really don't see a reason why I shouldn't use it with gentoo.
how can I change the block size, and how can I take care of correct alignment? (or is that what parted will do?)

I was just recompiling the kernel (3.0.0) and i stumbled over some options:

Baarn · n00b Joined: 02 Mar 2011 Posts: 17

Ok, i did a lot the last few days and learned some stuff.
But now i encounter another problem

Grub2 mkconfig wrote a config after some tweaking, and wrote it to the disks.
my problem now is, that grub2 used the UUID of the RAID-map /dev/md1
when booting, Grub tells me that there is no such device, of course not, RAID has not been initialized.

so how should i do this?
easies way (which i dont like)
drop raid on /dev/md1 and get UUID of /dev/sdc2 /dev/sdd2 respectively and write each grub with a modified grub.cfg onto the disks.

hard way
keep raid, and get the "before raided UUID" of each disks, modify grub.cfg and write to disk.
problem is: how to get the UUID of the non raided disks when in raid? or is there a way to get the UUID if the are not mounted?
next problem: there ist ext2 on the disks, but mount and parted tell me its a pseudo-raid filesystem, would this be a problem for grub to understand and find stuff?