[CentOS] EFI and RAID questions

[Dennis Jacobfeuerborn]

On 10.05.2014 19:17, Dennis Jacobfeuerborn wrote:
> On 10.05.2014 18:36, CS_DBA wrote:
>> Hi All;
>>
>> I have a new server we're setting up that supports EFI or Legacy in the bios
>>
>> I am a solid database guy but my SA skills are limited to what I need to 
>> get by
>>
>> 1) I used EFI because I wanted to create a raid 10 array with 6 4TB 
>> drives and apparently I cannot setup gpt partitions via parted in legacy 
>> mode (at least that's what I've read - is this true?)
> 
> When you say legacy mode do you mean BIOS or the CSM ("Compatibility
> Support Module") of the UEFI firmware?
> 
> BIOS cannot boot from GPT partition but the CSM mode of the UEFI
> firmware should be able to. You really want to go with plain UEFI though
> if your system supports it.
> 
>> 2) I installed the OS on 2 500GB drives, I used to do all my installs 
>> with software RAID (mirrored) without LVM as follows:
>> - create 2 raid partitions (one on each drive)  for swap, /boot and /
>> - create a raid1 device for each set of partitions above
>>
>> The installer would not let me proceed without a /boot/efi partition I 
>> tried to create a raid partition on each drive for this and create a 
>> /boot/efi raid disk but when I doit this way in the installer I no 
>> longer see the "EFI SYSTEM Partition" as an option for the filesystem 
>> type so this did not work either.
>>
>> I ended up doing hardware raid for the OS drives and software raid for 
>> the 6 4TB data drives. It works but I prefer to do software raid for 
>> everything so we ca have standard methods of monitoring for bad drives.
>>
>> Is there a way to setup software raid with EFI?
> 
> No. The UEFI Firmware needs to access to this partition before it can
> boot the OS so anything that needs to have the OS running (like a
> software raid) cannot work.
> What you can do is create the partition on both disks, point the
> installer to only the first disk and then later copy the files over to
> the partition on the other disk so that if the first disk dies you can
> still boot using the second one.
> The partition can be tiny (just a couple of megabytes), should be the
> first partition on the disk (though I think this is not strictly
> necessary), should be formatted as FAT32, and should be given a type
> GUID of "C12A7328-F81F-11D2-BA4B-00A0C93EC93B" which means "EFI System
> partition" so that the UEFI firmware can find it.
> 
> You *should* be able to create the other partitions (including /boot) as
> software raid though I've not done this myself yet so I'm not 100%
> certain on that.

Just to give you an idea what a "couple of megabytes" means this is what
is stored on my EFI partition right now:

[root at nexus EFI]# du -csh /boot/efi/EFI/*
658K	/boot/efi/EFI/Boot
7,8M	/boot/efi/EFI/fedora
244K	/boot/efi/EFI/fedora15
18M	/boot/efi/EFI/Microsoft
247K	/boot/efi/EFI/redhat
27M	total

That's with four different OS installations so for a non-dual-boot
system something like 50-100MB should be plenty.

Regards,
  Dennis