[CentOS] C7 + UEFI + GPT + RAID1

Alessandro Baggi

alessandro.baggi at gmail.com
Sat Mar 12 16:22:12 UTC 2016


Hi list,
I'm new with UEFI and GPT.
For several years I've used MBR partition table. I've installed my 
system on software raid1 (mdadm) using md0(sda1,sdb1) for swap, 
md1(sda2, sdb2) for /, md2 (sda3,sdb3) for /home.  From several how-to 
concerning raid1 installation, I must put each partition on a different 
md devices. I've asked times ago if it's more correct create the md 
device, partitioning it and create fs on each partition created on md 
device:

mdadm create /dev/md0 ...
fdisk /dev/md0:
md0p1 swap
md0p2 /	    xfs
md0p3 /home xfs

or create for each partition an md device and create the fs on mdX 
device directly:

mdadm create /dev/md[012].....
mkfs.fs /dev/mdX (for each md device)
md0 swap
md1 /
md2 /home

I got as answer that the second solution is the correct solution.

I'm installing C7 1511 on a skylake machine with UEFI and I'm confused.
After googling, for my installation I must create gpt table, 1 partition 
with fat32 type of 512M, and 2 partition for swap and / (I've excluded 
/home), clone gpt partition table on second disk with sgdisk, create md 
device for swap and /.

I've created gpt partition table with:

1) part1 512m fat32 EFI-part
2) part2 8gb raid  swap
3) part3 ~500gb raid /

then I've cloned gpt of sda to sdb without problem.

Then I've created array md0 for swap and md1 for / and then rebooted the 
system.

I've started installation process.
During disk selection I get only one disk tagged as MDRAID disk and not 
sda and sdb. Selecting MDRAID disk I can't see sda1 sdb1 EFI-part, md0 
and md1 devices.

Going to console, cat /proc/mdstat give me only md1. If I try to start 
md0 mdadm says sda2: not such file or directory but the partition exists 
on /dev/sda.
Coming back to Installer, it forces me to create partitions on MDRAID 
(md1) disk and I create:

md1p1 EFI
md1p2 swap
md1p3 /

Installation was performed an system booted.

Now, on this machine with mbr partition type I get md0 (sda1, sdb1) and 
md1 (sda2, sdb2)
on uefi machine with gpt I get md1 (sda, sdb).
I've tried also installing with mbr before using gpt, and I got md0 
(sda1, sdb1), md1(sdb2, sda2) and the other 2 partition for EFI as 
expected. But with mbr installer said me that It gpt was needed.

Why using gpt, if I set two raid partition, create 2 raid, rebooting it 
gives me that md1 has sda and sdb instead sda2 and sdb2 and other md is 
dead?

What is the correct method to install on RAID? 1 md device and create 
partition on it or N md devices for N partition?

Why using gpt I get only one disk on disk selection (mdraid device), not 
the 2 physical disk, and not the 2 md raid created?

Hope in help.

Alessandro.






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