Messages in this thread | | | Subject | RE: [RFC] Multi-path IO in 2.5/2.6 ? | Date | Tue, 10 Sep 2002 11:34:26 -0500 | From | "Cameron, Steve" <> |
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Alan Cox wrote:
> On Tue, 2002-09-10 at 15:43, Cameron, Steve wrote: > > Well, the BIOS can do it if it has one working path, right? > > (I think the md information is at the end of the partition,) > > Yes. A good PC bios will spot an hda boot fail, and try hdc. Good PC > bioses are alas slightly hard to find nowdays. In that set up raid1 > works very well. Multipath is obviously a lot more complicated.
For the failed primary path case yes. In the case the primary path is working, I would think booting from a multipath device and a RAID1 device would be very very similar, or even identical, from the perspective of the BIOS, right?
> > lilo and grub as they stand today, and anaconda (et al) as it > > stands today, cannot do it. They can do RAID1 md devices only. > > lilo for example will complain if you try to run it with > > boot=/dev/md0, and /dev/md0 is not a RAID1 device. At least > > It relies on the BIOS to do the data loading off the md0. In your > scenario you would tell it the boot is on /dev/sdfoo where that is the > primary path. I guess the ugly approach would be to add lilo/grub > entries for booting off either path as two seperate kernel entries. >
Hmm, I thought I had tried this, but, I had tried so many things. If anyone has successfully set up a system booting from a multipath md device, I'd like to hear about it.
What I tried was more or less this:
1. Install normally to disk-A, remove disk-A from the system. 2. Install normally to disk-B. Install disk-A into the system. and boot from disk-B. (now I can safely copy from disk-A, which has no actively mounted partitions.) 3. Create multipath devices on disk-C, one for each partition. The partitions are bigger than those on disk-A, to allow for md to put its data at the end. 4. Copy, (using dd) the partitions from disk-A to the md devices.
5. mount the md devices, and chroot to the md-root device. Try to figure out how to run lilo to make booting from disk-C possible also, initrd modifications to insmod multipath.o, mount the md devices, etc. This part, (making lilo work) I never was able to figure out.
Would boot up and say "LI" then stop... or various other problems that I can't quite recall now. (this was a couple weeks ago)
I guess this is getting a little off topic for linux-kernel, so maybe I should let this drop now, or take it over to linux-raid, but I _would_ like to hear from anyone who has got a multipath boot device working.
Anyway, even if this can be made to work, this leaves a rather ugly and convoluted method of installation.
> > bit, but so far, I am unsuccessful. I think grub cannot even do > > RAID1. > > Works for me
Ok, good to hear. (I had it only on hearsay that grub couldn't do it, so my experiments were confined to lilo.)
-- steve
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