[CentOS] raid 5 install

Thu Jun 27 17:27:50 UTC 2019
Robert Heller <heller at deepsoft.com>

At Thu, 27 Jun 2019 14:48:30 +0100 CentOS mailing list <centos at centos.org> wrote:

> I have done this a couple of times successfully.

> I did set the boot partitions etc as RAID1 on sda and sdb. This I believe is
> an old instruction and was based on the fact that the kernel needed access
> to these partitions before RAID access was available.

Actually *grub* needs access to /boot to load the kernel. I don't believe that
grub can access (software) RAID filesystems. RAID1 is effectively an exception
because it is just a mirror set and grub can [RO] access any one of the mirror
set elements as a standalone disk. Note that UEFI partitions can't be RAID at
all (and are FAT filesystems) and need to be accessable by the BIOS / boot
EEPROM. Once the kernel starts, the raid array(s) can be started, then LVM
volumes can be scanned for and set up, then the root file system mounted, and 
then the system is up and running -- all of that magic is handled in the 

So the rule of thumb is a "small" /boot/efi FAT file system (if using UEFI 
boot) a /boot mirror set, and the rest whatever RAID logic, probably with LVM 
on top of that.  Usually one creates a UEFI partition on both (or all three or 
more) disks -- they can't be a mirror set, but certainly can be rsync'ed 
regularly.  Then a smallish mirror set for /boot, than whatever is left used 
for the main system filesystem: RAID whatever, etc.  


> I'm sure someone more knowledgeable will be able to say whether this is
> still required.

Yes.  See above.

> Gary
> On Thursday 27 June 2019 14:36:37 Nikos Gatsis - Qbit wrote:
> > Hello list.
> > 
> > The next days we are going to install Centos 7 on a new server, with 
> > 4*3Tb sata hdd as raid-5. We will use the graphical interface to install 
> > and set up raid.
> > 
> > Do I have to consider anything before installation, because the disks 
> > are very large?
> > 
> > Does the graphical use the parted to set/format the raid?
> > 
> > I hope the above make sense.
> > 
> > Thank you in advance.
> > 
> > Nikos
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