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Redundanz
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PostPosted: Fri Sep 09, 2016 1:15 pm    Post subject: grub-install fails on southbridge RAID0 Reply with quote

Hi folks,

I am setting up an installation from the "Hybrid-DVD" and I am following the main handbook procedure.
Yet I have to say it is my first time with Gentoo/Funtoo. But I think my problem is not really very distro-specific anyway.

My machine is a MSI 790FX-GD70 (SB700 onboard RAID 0/1/10/5), AMD Phenom II 955, 4 GB RAM, 2x WD Raptor 74GB

So the process of installing goes without any major issues as far as to the section of installing grub2.
My RAID is visible in parted, blkid, fdisk -l ... (everything looks fine)
The RAID (dmraid) is configured as follows:

Code:
(CHROOT) livecd / # dmraid -ay
RAID set "pdc_hcgfdeeai" already active
RAID set "pdc_hcgfdeeai1" already active
RAID set "pdc_hcgfdeeai2" already active
RAID set "pdc_hcgfdeeai3" already active


Code:
(CHROOT) livecd / # parted /dev/mapper/pdc_hcgfdeeai print
Model: Unknown (unknown)
Disk /dev/mapper/pdc_hcgfdeeai: 149GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags:

Number  Start   End     Size    Type     File system     Flags
 1      1049kB  135MB   134MB   primary  ext2            boot, raid
 2      135MB   8725MB  8590MB  primary  linux-swap(v1)  raid
 3      8725MB  149GB   140GB   primary  ext4            raid



(btw i set the raid flags during my own troubleshoot, but i believe they do nothing in pseudo hardware raid!?! regardless they didnt change the behaviour, and every write/read up to the grub install was working fine anyway on the raid without the flags to begin with... question is if i should remove them again?)

So I am chrooted in the new env and when I try to install grub the following happens:

Code:
(CHROOT) livecd / # grub-install --target=i386-pc --no-floppy /dev/mapper/pdc_hcgfdeeai
Installing for i386-pc platform.
  Volume group "pdc_hcgfdeeai1" not found
  Cannot process volume group pdc_hcgfdeeai1
  Volume group "pdc_hcgfdeeai1" not found
  Cannot process volume group pdc_hcgfdeeai1
grub-install: error: disk `lvm/pdc_hcgfdeeai1' not found.


What I don't understand is why he is talking about volume groups. The verbose output (very long) contains the following excerpt at the very end:

Code:
grub-install: info: /dev/mapper/pdc_hcgfdeeai1 is not present.
grub-install: info: Scanning for DISKFILTER devices on disk host.
grub-install: info: Scanning for mdraid1x devices on disk host.
grub-install: info: Scanning for mdraid09_be devices on disk host.
grub-install: info: Scanning for mdraid09 devices on disk host.
grub-install: info: Scanning for dmraid_nv devices on disk host.
grub-install: info: Scanning for ldm devices on disk host.
grub-install: info: scanning host for LDM.
grub-install: info: no LDM signature found.
grub-install: info: Scanning for lvm devices on disk host.
grub-install: info: Scanning for DISKFILTER devices on disk proc.
grub-install: info: Scanning for mdraid1x devices on disk proc.
grub-install: info: Scanning for mdraid09_be devices on disk proc.
grub-install: info: Scanning for mdraid09 devices on disk proc.
grub-install: info: Scanning for dmraid_nv devices on disk proc.
grub-install: info: Scanning for ldm devices on disk proc.
grub-install: info: scanning proc for LDM.
grub-install: info: no LDM signature found.
grub-install: info: Scanning for lvm devices on disk proc.
grub-install: info: drive = -1.
grub-install: error: disk `lvm/pdc_hcgfdeeai1' not found.


I didnt set up lvm, did I ?!?!
And the lvm service itself seem to be stuck in a strange state. Because it cant be stopped or started ("lvm is already starting"...)
The RAID array shouldnt have anything to do with LVM at this state. I didnt set up LVM...

Why is Grub not just dumb-mode accessing the mapped drive and writes the MBR?
Is it a grub problem?
Did I miss something essential when setting up the raid that has to be mounted/enabled in the chrooted environment specifically?

Trying to write grub to the drives /dev/sda or /dev/sdb (the two drives in the raid) gives EXACTLY the same error as above when addressing the mapper raid device. -> With the volume group dev/mapper/pdc_hxyz...... not being found... which is strange enough, to me.

Just as a side note, my experience with unix-based systems is average, I am not a total beginner, I used CentOS, SUSE and Ubuntu long times ago.
But somehow I stopped using Linux over the last 4-5 years an have to admit I'm a bit rusty. So throw everything at me what there is to do but I am not the best in spotting the details/holes by myself.

Please tell me which additional outputs you would need me to provide you, I just didn't want to blow up the first post with too much i/o stuff already.

This setup has to work, I used those components with the same raid0 setup on an older ubuntu several years ago.
It seems to be a very special problem though (apart from many people having trouble setting up raid0 to be initialized correctly of course).

Thanks for any suggestions in advance!
Cheers.
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Redundanz
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PostPosted: Fri Sep 09, 2016 7:26 pm    Post subject: Reply with quote

post script:

What a coincidence...I just noticed that this thread

https://forums.gentoo.org/viewtopic-t-1050746.html

is right below mine and focuses on a very similar, yet not the same problem. (And that after searching 3 separate forums for my problem yesterday...)
I took the advice given inside that thread into consideration but so far no success.

It may be the same core issue that me and the other thread starter has.
But he is using LVM and not raid
And I am using raid and not lvm / LUKS
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NeddySeagoon
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PostPosted: Fri Sep 09, 2016 8:24 pm    Post subject: Reply with quote

Redundanz,

It looks like you have fakeraid. This topic may help.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.
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frostschutz
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PostPosted: Fri Sep 09, 2016 9:00 pm    Post subject: Reply with quote

If it's Linux only and not a dualboot system, you should avoid dmraid and stick to mdadm.

And think twice about raid0.
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Redundanz
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PostPosted: Sat Sep 10, 2016 2:39 am    Post subject: Reply with quote

thanks for your answers.

i chose to backup the environment... disable the array in the bios and move the environment to one of the disks to finish installing.
will finish setting up the machine and take care of it later.

actually i'm pretty interested in the performance difference (if significant at all) of linux software raid0 vs. bios controlled raid0.
so in the end i will need to set them up both working.
will post in this sub-forum if i know what was the problem. for future reference.

(i managed that SB700 raid install on Xubuntu once... with grub, years ago, so it just has to work ... somehow)
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frostschutz
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PostPosted: Sat Sep 10, 2016 8:52 am    Post subject: Reply with quote

Redundanz wrote:
actually i'm pretty interested in the performance difference (if significant at all) of linux software raid0 vs. bios controlled raid0.


bios raid is software raid, just with a bios interface to create the on-disk metadata. all of it is still done in software. there could still be performance differences since the implementation is slightly different, but it's not like there is any dedicated raid hardware at work. there is none.

you'll find more people using mdadm than dmraid. and mdadm is more flexible and lets you combine things, you can stick to raid1 with 0.90/1.0 metadata for the /boot partition (simplifies things for the bootloader), and use raid-whateveryouwant with 1.2 metadata for everything else.

but in your case it sounds like you might prefer separate partitions or LVM over raid0.

raid0 does not improve performance except for cases that don't matter (large linear reads/writes as opposed to random i/o)
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Redundanz
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PostPosted: Sat Sep 10, 2016 8:53 pm    Post subject: Reply with quote

So if I use this machine to record encoded video which I stream to an nginx rtmp app running on this machine... do you think raid0 will improve performance over jbod/single disk?
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frostschutz
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PostPosted: Sat Sep 10, 2016 11:30 pm    Post subject: Reply with quote

Is your network stream / bandwidth faster than a single of your HDDs? If not then no.

What else is running on the box? If there are performance issues due to other I/O, dedicating one disk for recording use and using the other disk for the other stuff might help more than RAID.
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