Re: RAID b/w GPT and NON GPT partition.

[Pascal Hambourg <pascal@plouf.fr.eu.org>]

Gary Dale a écrit :
> On 30/06/15 02:36 PM, Muhammad Yousuf Khan wrote:
>>
>> should i create partition 2 of a size of 1 GB. and make it as a boot 
>> partition and install grup on that partition. [...]
>
> I've stopped using separate boot partitions since wheezy, which allowed 
> systems to boot directly from a RAID array.

To make it clear, we are talking about a "BIOS boot" partition, not a
/boot partition.

> I've found boot partitions 
> provide no real benefit on any computer less than a decade old.

Well, I can list two situations which benefit from a separate /boot.

1) When booting from BIOS on a GPT-style disk larger than 2 TiB, a
separate /boot partition located beyond the 2 TiB limit ensures that the
boot loader, which relies on BIOS functions to access the disk, is able
to read all the required files in /boot when the root filesystem may
extend beyond the 2 TiB limit. This is of course not required when
booting from UEFI. You may argue that no-one is fool enough to create a
root partition of more than 2 TiB and I would agree, but think about an
LVM physical volume spanning over the whole disk and containing the root
logical volume among other logical volumes. Quite a usual layout, isn't
it ? If the PV lays beyond the 2 TiB limit, there is a chance that the
root LV uses blocks beyond the 2 TiB limit and that filesystem meta-data
or files needed to boot are stored in blocks beyond the 2 TiB limit.

2) GRUB 2's core image can include modules to read /boot on RAID and LVM
volumes, so a separate plain /boot partition is not required any more.
However, I have experienced weird behaviour of GRUB 2 with a dangling
RAID 5 member disk : a disk becomes unresponsive, marked as failed on
other RAID members ; after reboot, the disk is back, GRUB finds one more
active disk than expected and refuses to assemble the array, so boot
fails until the disk is actually unplugged or disabled in BIOS settings.

> Partition numbers have no intrinsic meaning. They just identify the 
> partition and, as you have seen, have nothing to do with the layout of 
> the disk (in your case 1,5,3,4).  You can call your new ef02 partition 
> "2" or any other unused single-digit number (yes, you could call it 20 
> or 111, but why bother?).

The partition number is the index of the partition entry in the
partition table.