Re: [gentoo-user] RAID 1 on /boot

["J. Roeleveld" <joost@antarean.org>]

On Sat, February 22, 2014 06:27, Facundo Curti wrote:
> Hi all. I'm new in the list, this is my third message :)
> First at all, I need to say sorry if my english is not perfect. I speak
> spanish. I post here because gentoo-user-es it's middle dead, and it's a
> great chance to practice my english :) Now, the problem.

First of all, there are plenty of people here who don't have English as a
native language. Usually we manage. :)

> I'm going to get a new PC with a disc SSD 120GB and another HDD of 1TB.
> But in a coming future, I want to add 2 or more disks SSD.
>
> Mi idea now, is:
>
>     Disk HHD: /dev/sda
> /dev/sda1 26GB
> /dev/sda2 90GB
> /dev/sda3 904GB
>
>     Disk SSD: /dev/sdb
> /dev/sdb1 26GB
> /dev/sdb2 90GB
> /dev/sdb3 4GB
>
> And use /dev/sdb3 as swap. (I will add more with another SSD in future)
> /dev/sda3 mounted in /home/user/data (to save data unused)

Why put the swap on the SSD?

> And a RAID 1 with:
> md0: sda1+sdb1    /
> md1: sda2+sdb2    /home
>
> (sda1 and sda2 will be made with the flag: write-mostly. This is useful
> for
> disks slower).
> In a future, I'm going to add more SSD's on this RAID. My idea is the
> fastest I/O.
>
> Now. My problem/question is:
> Following the gentoo's
> doc<http://www.gentoo.org/doc/es/gentoo-x86+raid+lvm2-quickinstall.xml>,
> it says I need to put the flag --metadata=0.9 on the RAID. My question is
> ¿This will make get off the performance?.

metadata=0.9 might be necessary for the BIOS of your computer to see the
/boot partition. If you use an initramfs, you can use any metadata you
like for the root-partition.

> I only found this
> document<https://raid.wiki.kernel.org/index.php/RAID_superblock_formats#The_version-0.90_Superblock_Format>.
> This says the difference, but nothing about performance and
> advantages/disadvantages.
>
> Another question is, ¿GRUB2 still unsupporting metadata 1.2?

See reply from Canek.

> In case that metadata get off performance, and GRUB2 doesn't support this.
> ¿Anyone knows how can I fix this to use metadata 1.2?
>
> I don't partitioned more, because I saw this unnecessary. I just need to
> separate /home in case I need to format the system. But if I need to
> separate /boot to make it work, I don't have problems doing that.
>
> But of course, /boot also as RAID...

/boot seperate as RAID-1 and metadata=0.9 and you are safe.

> ¿Somebody have any ideas to make it work?

It is similar to what I do, except I don't have SSDs in my desktop.

I have 2 partitions per disk:
1 : /boot (mirrored, raid-1)
2 : LVM (striped, raid-0)
All other partitions (root, /usr, /home, ....) are in the LVM.

I use striping for performance reasons for files I currently work with.
All important data is stored and backed up on a server.

For this, an initramfs is required with support for mdraid and lvm.

> Thank you all. Bytes! ;)

You're welcome and good luck.

Please let us know what the performance is like when using the setup you
are thinking off.

--
Joost