>________________________________
> From: Nico Kadel-Garcia <[log in to unmask]>
>To: Nico Kadel-Garcia <[log in to unmask]>; James M. Pulver <[log in to unmask]>; "[log in to unmask]" <[log in to unmask]> 
>Sent: Tuesday, 14 April 2015, 3:02
>Subject: Re: need SSD RAID controller advice
> 
>
>On Mon, Apr 13, 2015 at 8:16 PM, Konstantin Olchanski
>
>
>
>
><[log in to unmask]> wrote:
>> On Mon, Apr 13, 2015 at 07:29:18PM -0400, Nico Kadel-Garcia wrote:
>>> > I am not sure what you refer to. With SL5 and SL6 you have 2 disks,
>>> > put "/" on a software RAID1 partitions put grub on both disks ...
>>>
>>> Until it fails. Grubby, along with the kernel installlation RPM,
>>> doesn't know how to update, manage, or keep synchronized this second
>>> /boot partition. Hilarity can then ensue, along with making sure that
>>> your /etc/fstab doesn't detect the wrong disk and mount it incorrectly
>>> as /dev/sda. See, if your first disk dies, unless you're very cautious
>>> with /etc/fstab, it's very much a crapshoot if hte right partition
>>> will mount as "/boot".
>>>
>>> Been there, done that, gave up on the silliness.
>>>
>>
>> You talk about /boot, /dev/sda, grubby, etc, I doubt you have been there, done that. Gave up, sure.
>>
>> With mirrored disks, there is only /dev/md0 ("/"), /dev/md1 (swap), etc (if you have /home, /data, etc),
>> in /etc/fstab, "/" is mounted by UUID of the /dev/md0 RAID1 device,
>> which in turn is assembled by UUID of component disks using mdadm magic.
>
>Been there, done that. Don't have to make this stuff up, I spent some
>time *designing* Linux based storage servers, but it was more than 5
>years ago.
>
>However, software RAID may have improved to the point where "/boot"
>doesn't have to be its own partition. So I just tried it on a VM
>runing SL 6.6, and got "unhandled exception", and git it to work
>flawlessly when I made "/boot" its own, non-RAID partition.. So I'm
>not filled with confidence that putting /boot on its partition is not
>
>still necessary.
>
>
>Are you finding that it actually works? Would you please post an
>/etc/fstab from a working system to help verify that it works?
>


More cutting edge linux distributions such as Ubuntu can have /boot as part of a RAID system, and even on an LVM. I think this is a feature of GRUB2. If you wish to RAID /boot on older dists (AFAIR this applies to SL5 and SL6), you can RAID it but it must be mirrored. AFAIK GRUB doesn't understand the RAID but it looks sufficiently like a regular partition/filesystem that it is able to find what it needs. I don't have a fstab to show you from an older config as I migrated to Ubuntu Server for my Xen machines. I thoroughly tested both these configurations and the machine is able to fully boot with any given drive removed.

Here is an Ubuntu one, plus supporting information, FWIW...


# cat /etc/fstab
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
proc            /proc           proc    nodev,noexec,nosuid 0       0
/dev/mapper/xen2-root /               ext4    errors=remount-ro 0       1
/dev/mapper/xen2-swap none            swap    sw              0       0



# cat /proc/mdstat 
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
md0 : active raid5 sdc1[2] sda1[0] sdb1[1]
1953258496 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/3] [UUU]

unused devices: <none>
root@xen2:~# pvs
PV         VG   Fmt  Attr PSize PFree 
/dev/md0   xen2 lvm2 a-   1.82t 53.18g

root@xen2:~# lvs
LV              VG   Attr   LSize   Origin Snap%  Move Log Copy%  Convert
--- snip ---
root            xen2 -wi-ao 279.39g 
swap            xen2 -wi-ao   7.45g
--- snip ---





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