Re: Booting Software RAID

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On Mon, Jan 27, 2014 at 2:50 PM, <m.roth@xxxxxxxxx> wrote:

> Adrian Sevcenco wrote:
> > On 01/27/2014 08:42 PM, Les Mikesell wrote:
> >> On Mon, Jan 27, 2014 at 12:33 PM, Adrian Sevcenco
> >> <Adrian.Sevcenco@xxxxxxx> wrote:
> >>>
> >>> for quite some time (since 5.x era) i use
> >>> http://wiki.centos.org/HowTos/Install_On_Partitionable_RAID1
> >>> (with 6.x i don't even need the patch to mkinitrd)
> >>>
> >>> the mbr or whatever it is is written in /dev/md_d0 .. and thats it
> >>> in bios you put both hdd to boot and if the first have a problem the
> >>> second will boot, mail you that you have a degraded raid and start
> >>> resync after you replaced the drive. (and you can do it live)
> >>
> >> Does that all work the same for drives > 2 TB?
> > i have no idea .. it should .. my use cases at work are the boot drives
> (all under 500 GB)
> > and home (but i have no hdd > 2 TB)
> >
> > basically it is a raid over a block device so it does/should not matter
> > what you write into it...
> >
> As I noted in a previous post, it's got to be GPT, not MBR - the latter
> doesn't understand > 2TB, and won't.
>
> On a related note, what we've started doing at work is partitioning our
> root drives four ways, as they're now mostly 2TB that we're putting in,
> instead of three: /boot, swap, and /, with that as 1G, 2G, and 500G, and
> the rest of the drive separate. We like protecting /, while leaving more
> than enough space for logs that suddenly run away. At home, I'll probably
> do less for /, perhaps 100G.
>


There are few reasons why /boot should be on a partition/array >= 2TB.

GRUB doesn't support software raid levels other than 1 (sort of).  It
accesses one of the "mirrored" partitions and not the raid array itsself.
 So having large disks and only being able to use raid1 isn't often optimal
either.

While 100MB was fine in the CentOS 5.x days, it only takes 512MB or so with
CentOS 6.x to store a few Linux kernels (and other items - initrd,
initramfs, etc).

Once we have GRUB2, then it could be possible to boot from LVM.
But partitioning /boot separate from rootfs is not a big deal.



>
>        mark
>
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Mike
//  SilverTip257  //
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