On Aug 28, 2014, at 12:37 PM, Lars E. Pettersson <lars(a)homer.se> wrote:
On 08/28/14 20:21, Bruno Wolff III wrote:
> On Thu, Aug 28, 2014 at 11:10:54 -0700,
> Rick Stevens <ricks(a)alldigital.com> wrote:
>>
>> I think you need to reserve some small space on all the drives (and
>> with 3TB drives you can afford to sacrifice a few MB), use the remainder
>> as your RAID, and let the system put the boot partition in that reserved
>> space on the primary drive (the one the BIOS sees as the boot drive).
>
> I think using raid 1 (with the 1.0 header format) can work well for
> that. There can still grub issues with having a boot just work, but at
> least you have the stuff you need available.
Yes, that was my intention, raid1 for /boot and raid6 for / Accidentally I set /boot also
to raid6 :) But that can be fixed.
Or do n-way raid1, which will cause /boot to have as many copies as you add member
devices.
On my old system I use 1TB disks, with /boot as raid1, and grub boot-loader installed on
all disks. On that one I can boot the system from any of disks. Which is quite handy.
That's still possible whether /boot is raid1 (n-way or mirror), or raid6. Anaconda
will run grub2-install against all member devices that have a /boot member device (or at
least it should, I have recently done 2 drive testing on this).
Post install you can
grep -i grub2-install /var/log/anaconda/program.log
And it will show you the command used. It should list all member devices. So long as each
member drive has a BIOS Boot partition, grub2-install will find it automatically and
insert core.img there, as well as the specific jump code in the first 440 bytes of the
(protective) MBR to find it.
The problem here seem to be that due to the disks being large (larger
than 1TB) they are setup as GPT (GUID Partition Table), and they then also need a BIOS
boot partition to work on non UEFI based systems (if I have understood it correctly).
MBR partition entries are 32-bit so they're limited to 2TB. There's a small
advantage to using GPT in that there's a backup header and table. So long as your BIOS
doesn't get fussy with GPT, it's fine to use it even on 1TB drives, but it's
not necessary.
So, to be able to boot from any of the disks, I need a BIOS boot
partition on all disks, but anaconda seem to only install it on one of the disks (i.e. I
want the exactly identical partition tables on all disks).
It's messy. Again the installer should leave the user out of this entirely. You
don't need a BIOS Boot that's exactly 1MB in size, so if you don't want to
start from scratch but there's at least 100K free space on each member drive, you can
create a BIOS boot there and then rerun grub2-install against all the drives, e.g.:
grub2-install /dev/sd[abcde]
To know for sure how big of a BIOS Boot you need:
ls -lh /boot/grub2/i386-pc/core.img
Mine's 26KB, as my boot fs is XFS, without LVM or raid. Yours will be a bit bigger to
include mdraid1x.mod and raid6rec.mod and anything else that gets pulled in. I bet
it's much less than 100K actually.
Chris Murphy