raid0 root partition setup? (mdadm not making nodes)

barfo · Apprentice Joined: 04 Mar 2006 Posts: 163

so i recently picked up some new drives and thought i'd try going amd64 and running the OS from a software raid0 partition. i stuck with a very simple partition scheme, 1G /boot - raid1, 1G swap, the rest dedicated to / (318G) raid0. i used the latest amd64 livecd and created the partitions (type 0xFD), chrooted and set things up. to be on the safe side, i made two kernels - one my config the other a genkernel with everything in it. in both i compiled in support for the chipsets, raid and raid1 & raid0. i added mdadm to the default level, setup mdadm.conf as per instructions - in my case a very simple two line entry for /dev/md1 & /dev/md3.

i installed grub, setup both mbrs, added support for the genkernel initramfs image to the genkernel entry, had root=/dev/ram0 & real_root=/dev/md3 (it's the third partition on both drives) while the other kernel simply had the kernel name and root=/dev/md3.

when i attempt to boot either kernel i'm told that /dev/md3 is not a valid mount point. as far as i can tell, mdadm is not creating the device nodes (they aren't there when i use the livecd and chroot the system anyway) however i see output from mdadm as it boots and see nothing alarming in it - however no remarks concerning the partitions it should set up. i've chrooted a couple times now and do the same mknod'ing as is suggested in the various docs i've read. inside the chroot it all seems to work fine, but when i try to boot - no dice.

any ideas?

NeddySeagoon · Posted: Sun May 06, 2007 2:04 pm Post subject:

barfo,

mdadm in the defualt runlevel cannot be used for booting since its on the root partition, which must be read to run mdadm. It follows that /dev/md3 must exist and the raid0 be up to allow it to mounted.

Boot normally and watch for a line that says something like

barfo · Apprentice Joined: 04 Mar 2006 Posts: 163

thanks for the pointers neddy

i have not seen anything about autodetecting raid -but i'll have to look again next time i play with it. i do have udev in my kernel line entry in grub however. i'm certain however that the partitions are type 0xfd and that raid0&1 are compiled in - not modules. i see messages indicating that raid0,1,5... are there as genkernel pulls in all the types i do not need. however i _know_ raid0 & 1 are compiled in. and i've not seen any messages about inconsistent superblocks during any of the setup. when i reboot from the cd i can reassemble the array and all is perfectly happy.

do i have to do anything so that udev runs correctly? i'm using the latest stage3...

this is my first venture into raid - so forgive me if i'm overlooking something basic. i did find a post where a user mentioned that he'd had /dev/* tarred on shutdown so that the nodes would be there when he rebooted - but that sounds like a work-around.

NeddySeagoon · Posted: Sun May 06, 2007 3:23 pm Post subject:

barfo,

Old versions of udev did not make /dev/mdX entries but it should all just work now.
I set my system up a few years ago using raidtools.

Since kernel 2.6.13, when devfs was removed, the udev on the kernel line is no longer needed.
_________________
Regards,

NeddySeagoon

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

barfo · Apprentice Joined: 04 Mar 2006 Posts: 163

i'll pick over the kernel with a fine tooth comb again... it'll be a week before i try to repair it.

so if i understand you correctly, if i described things accurately, they should "just work" - is that correct? i can't believe i missed something in the kernel, but i'll double check.

thanks for the info

NeddySeagoon · Posted: Mon May 07, 2007 3:06 pm Post subject:

barfo,

Partition types (0xfd)
Raid personalities, raid0 and raid1
Persistant superblocks on your raid sets
root filesystem support
High level Disk Driver support (SCSI and/or IDE disk)
Low level Disk Driver, (for your disk chipset)

Is all you need to get it to boot
_________________
Regards,

NeddySeagoon

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

barfo · Apprentice Joined: 04 Mar 2006 Posts: 163

ok - thanks neddy!

it was really surprising to see that for some reason the kernel config lacked sata support compiled-in. i didn't check this as i assumed if anything genkernel wouuld put that in along with the kitchen sink and everything else it shoehorns into place.

it's now at least booting. i have a few other small fires to put out, but i'm very glad to see it's able to boot.