"--assemble --scan" support for imsm

[ added linux-raid with permission ]

There is no website. My personal thought is that we should extend the content at raid.wiki.kernel.org.

No, the auto-assemble I mentioned in the pull request will not avoid having an initrd. You are thinking of "in-kernel autodetect" which is not supported with the imsm metadata format (or any metadata format besides the md-v0.90 format). In general assembling arrays in userspace is much more flexible which is why you see the in-kernel autodetect code has been put in a no-new-features/maintenance-only mode.

I know Fedora and OpenSUSE have added support for this configuration to their initrd tools.

One of the primary benefits of using the Intel(R) RST (mdadm-imsm) format is that you can use the platform bios option-rom to boot from raid. So grub, grub2, lilo, or any other bootloader can boot from raid.
This is because the option-rom installs a bios int13 handler that
allows the bootloader to read from a raid volume as if it were a standalone disk.

The "mdadm -As" command will search all available disks and automatically assemble all the imsm arrays that it finds.

I think the 'fakeraid' moniker is tired and misplaced when referring to this new functionality in md/mdadm. There is nothing fake about Linux software RAID. I prefer "bios-raid" or even "software raid".

Current platforms ship support for raid levels 0, 1, 10, and 5.

Supported.

Like I mentioned above, the bootloader does not need any special code to boot from a bios-raid array because it can use standard int13 services.

Regards,
Dan

I have updated raid.wiki with the external metadata information a few weeks back. Please take a look and let me know if additional information is required. Thanks!

Dear Mr. Williams,

Thank you *very* much... you added very valueable pieces to my imsm RAID(-0) puzzle.

I just used the term "fakeraid" because it is *short* :) ... I did not mean it negative. Plus a lot of people use this term:
https://secure.wikimedia.org/wikipedia/en/wiki/RAID#Firmware.2Fdriver-based_RAID_.28.22FakeRAID.22.29
The Ubuntu FakeRAID HowTo
ArchLinux FakeRaid Howto

I would really like a new point on the raid-wikis first page named along these lines:
"[Intel] Firmware-based/BIOS-supported RAID ("FakeRAID")"
And I can do this if you want (aready created account yesterday).

On there should be a
- short description about what what a "fakeraid" is
- then for INTEL the info you get when you google for "intel linux raid"
- the info from Dan's answer below. Especially the part with "the
option-rom installs a bios int13 handler" (because there /is/ confusion about that out there :).
- Also the answer to the belows question: "How to install a bootloader"
should be on there.

And of course the more technical details the better. Eg.
- that (and maybe why) the primary partitions setup within the imsm
raid(-0) will be created on the first physical drive (/dev/sda), but not on the other drives.
- maybe even more in depth details on the external metadata format
- maybe some commonly used commandlines for mdadm and dmraid to check
the raid status ... or at least links to their howtos/wikis...

You mentioned:

2 questions:
a) What does RST stand for?
b) Does the (mdadm-imsm) mean, that the device-mappers "dmraid -f isw"
does not the same (or does intel just officially only support mdadm imsm?)

And finally: Can anyone tell me which solution:
dmraid -f isw
mdadm with imsm container support
is better in the sense:
- faster (higher throughput)
- less load (e.g. on cpu)
- more stable
- more features
I already posted this question to the [email protected] mailing list but (afaik) never got an answer.

Also: What I find odd with the dmraid solution: In fdisk it shows you e.g. /dev/dm-0p6, but there is no /dev/dm-0p6, there is only /dev/dm-0 to /dev/dm-11 and many /dev/mapper/LONGNAME symlinks to the /dev/dm-*. But the /dev/mapper/Volume_HASH_06 points to /dev/dm-4 ?!.... IMHO: total mess.

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"How to install a bootloader"?

You mentioned:

Which sounds great, but I can send you the chatlog from the #grub channel this morning... they don't seem to have an idea about that.

Could you/someone be so kind to provide me with the steps to manually install grub (legacy v0.97) or grub2 (v1.98) on a linux that accesses the raid via mdadm-imsm (/dev/md126, /dev/md127)?

Because for me it seems: "Intel" says: grub, gub2: No problem. "Grub" says: ???
I know that this is not a grub mailing list, but maybe just a small hint? Like: What should be in /boot/grub/device.map?
/dev/md126?
Do I install grub to the container (/dev/md127) or to the volume (/dev/md126)?
E.g.
- grub legacy gave me a "Error 22" on "setup (hd0)" with "/dev/md126 as (hd0) in device.map
- grub2: 1st it seems unclear what should be in the /dev/md, because grub assembles /dev/mdadm raids (independent of the BIOS), 2nd it seems unclear how this internal mdadm assembly interferes with "accessing the RAID via the int13 handler as a standalone disk"
- lilo: I would prefer a grub based solution

Again: Maybe this information is somewhere out there, but that's the problem: There are bits and pieces [about Intel BIOS supported RAID imsm] all over the place --> That's why I would love to (help to) create this wiki page I mentioned earlier to just assemble the most basic things in one place. .. Also that next time a guy like me (with a lot of half-knowledge ;) comes along and asks many "stupid" questions about imsm integration you can hopefully just point him to this wiki page.
Does this make sense to you too?

Any hint will be greatly appreciated!

K. Posern

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