dmraid volume mapping

gspellini · n00b Joined: 18 Sep 2009 Posts: 3

Ciao, ho un problema nel boot di gentoo da un array RAID0 creato via LSI utility (RAID software ICH9R/DO).
Il server monta i seguenti pacchetti:
gentoo-sources-2.6.30-r6
dmraid-1.0.0_rc15-r1
device-mapper-1.02.28
genkernel-3.4.10.906
grub

La mappatura dei volumi avviene sui nodi /dev/mapper/ddf1_xxxxx

Il problema è:
ad ogni reboot il sistema assegna un diverso UUID ai volumi. Di conseguenza non viene trovata la root directory impostata in grub.conf e le partizioni definite in /etc/fstab.
Il boot si blocca e permette la shell. Inserendo manualmente il nuovo nome volume (/dev/mapper/ddf1_nuovoID_root), il boot procede regolarmente.

Come si fa a mantenere fisso il nome dei volumi in /dev/mapper/ ?

posto grub.conf

default 0
timeout 30
#splashimage=(hd0,0)/boot/grub/splash.xpm.gz

title Gentoo Linux 2.6.30
root (hd0,0)
kernel /boot/kernel-genkernel-x86-2.6.30-gentoo-r6 root=/dev/ram0 real_root=/dev/mapper/ddf1_4c53492020202020808627c3000000003831ca55000014503 dodmraid
initrd /boot/initramfs-genkernel-x86-2.6.30-gentoo-r6

Grazie

NeddySeagoon · Posted: Sat Sep 19, 2009 1:52 pm Post subject:

gspellini,

The language of the main forums is English. I don't read Spansh but the I can follow what you have done.

Did you tell genkernel to include dmraid when you built your kernel and initrd ?
If not, its missing from the initrd.

genkernel builds its own version of dmraid - which may be different from the version that emerge dmraid gives you.

Lastly, the only reason for using dmraid on Linux is that the raid set must be shared with Windows.
Your ICHx raid is known as fakeraid because it looks like hardware raid but its another version of software raid.
Kernel raid is more robust than dmraid but the switch is a reinstall.
_________________
Regards,

NeddySeagoon

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

gspellini · n00b Joined: 18 Sep 2009 Posts: 3

NeddySeagoon,
thanks a lot,
my language is italian and I have many difficult to explain in English the problem, sorry.
I included the dmraid in kernel and in initrd to, if I did't the system could not started.
The problem is the different UUID of the volume at every reboot,
I can't anderstand why the kernel generate time after time a different UUID for the same volume.
Maybe I will follow your second way and will reinstall with mdadm.
I ask you a question, why you said that mdadm is better than dmraid over ICHx?
thanks and sorry for my incredible english.

NeddySeagoon · Posted: Sun Sep 20, 2009 1:38 pm Post subject:

gspellini,

Lets stick to English - your English is much better than my Italian.

Your Intel ICH9R chipset is not a hardware raid controller. It relies on software. Some of which is in the BIOS, some of which is in the kernel and some of which is in the dmraid external kernel module. If/when you get a problem with your hardware and which to recover the data on your raid, you need the same hardware and same BIOS to do it as the data placement on the drives are controlled by these items.

Kernel raid is completely portable - you plug the drives into new hardware of any sort and provided the kernel has raid support, it just works. Further, the kernel version of raid is more mature than dmraid. Its been around much longer. There are few performace differences except possibly in raid1, when kernel raid tries to read from all the mirror copies to provide faster reads. Thats not in dmraid yet.

Gentoo does not support mounting by UUID anywhere without patches, not just with dmraid.

If you are not comfortable with your English, you can post in our Italian Fourm
_________________
Regards,

NeddySeagoon

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

gspellini · n00b Joined: 18 Sep 2009 Posts: 3

Thank you NeddySeagoon,
It's my first time in the forum and I don't now very well the policy and others.
I will follow your tips, I ask you only a last question: there is a best one file system
for a mdadm raid0 solution? (I suppose have to be trasparent and I use reiserfs for every one partition)
bye
gio

NeddySeagoon · Posted: Mon Sep 21, 2009 9:07 pm Post subject:

gspellini,

There is no such thing as a best filesystem. They all have good points and weak points.
When you use kernel raid and mdadm to set up your raid. You can have several raid sets on the same drives with different raid levels and different filesystems.

Indeed, you must. You cannot boot from a kernel/mdadm raid0 set as grub ignores raid. You must either make /boot raid1, or not raidied at all.
With mdadm, you partition the drives (identically) then use mdadm to form the partitions into raid sets.
If you have /dev/sd[ab]1, that can be /boot, raid1 with ext2, /dev/sd[ab]2 can be swap, not raided ... the kernel will manage the swaps for itself.
/dev/sd[ab]3 can be the extended partition. Then you can can make more partitions and more raid sets at different raid levels using different filesystems.
_________________
Regards,

NeddySeagoon

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