[TriLUG] SL (RHEL) 7 installed on software-RAID1 (mirrored) drives

[Dwain Sims]

Comments below

Dwain


---------- Forwarded message ----------
From: David Burton <ncdave4life at gmail.com>
To: Triangle Linux Users Group General Discussion <trilug at trilug.org>
Cc:
Date: Sat, 8 Nov 2014 03:21:17 -0500
Subject: [TriLUG] SL (RHEL) 7 installed on software-RAID1 (mirrored) drives
I decided to set up a new server. I started with an AMD Turion X2 based
laptop with two SATA drive bays. (It used to have Windows Vista on it.) I
installed a pair of 160GB blank drives in the two bays (one Seagate and one
WDC),

Are spinning disks or SSD?  I would be somewhat suspicious that you have
slightly different drive geometry since they are not identical (either way).

Are you using a RAID controller?  Or is there RAID built on to this
motherboard?

Or is this some sort of software RAID (it does not sound like it from your
description).

 and set out to install Scientific Linux 7.0 on a RAID 1 (mirrored)
configuration.

The first hiccup was that the installer was apparently incapable of setting
up the two drives for RAID1.

If it is hardware RAID of some sort, I would not expect the installer to
set that up for you.  Likely from the BIOS or a separate utility.

So I booted from a PartedMagic CD, and used it to do the partitioning, and
created the RAID1 array.

That sounds more like software RAID, though?  Is this LVM doing the
mirroring?

 (I partitioned the two drives identically,
reserving 3GB on each drive for a Linux Swap partition.) Then I booted the
SL DVD, and tried the install again. It recognized the RAID1 array,
formatted it for ext4, and installed smoothly (though I did a lot of
guessing on the "Software Selection" screen).

At this point, the machine seemed okay. I shut it down, started it again,
and it was fine.

So far so good. So then I tested the RAID1 functionality: I shut down the
computer, removed one of the drives, and tried to boot it.

I was expecting it to display some error messages about the RAID array
being degraded, and then come up to the normal login screen. But it didn't
work. Instead I got:

Welcome to emergency mode! After logging in, type "journalctl -xb" to view
system logs, "systemctl reboot" to reboot, "systemctl default" to try again
to boot into default mode.
Give root password for maintenance
(or type Control-D to continue):

The same thing happens regardless of which drive is missing.

That's no good! The purpose of the mirrored drives is to ensure that the
server will keep on running of one of the drives fails.

Ctrl-D just gets me back to a repeat of the same "Welcome to emergency
mode" screen. So does entering my root password and then "systemctl
default".

*Does anyone have any suggestions for how to make this thing boot & run
"normally" (with a degraded RAID1 array) when a drive fails?*

As it stands, it appears that installing on RAID1 mirrored drives will just
double the chance of a drive failure bringing down the server. That is *not*
what I was hoping to achieve w/ mirrored drives.

Two other notes:

1. I'm seeing some apparently-innocuous errors:
  ATA*x*: softreset failed (device not ready)
The "*x*" depends on which drives are installed. I get more of those errors
with two drives installed than with only one.

2. At the "Software Selection" screen I didn't know what to pick, so I
chose:
"General Purpose System" +
  FTP Server
  File and Storage Server
  Office Suite and Productivity
  Virtualization Hypervisor
  Virtualization Tools
  Development Tools

Should make no difference.