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Re: Any advice for a user about to use LVM for the first time?



Kevin O'Gorman wrote:
> Bob Proulx wrote:
> > For people adding additional mdadm raid volumes later they need to
> > do some configuration for it.
> 
> This is exactly my case.  I'm installing a RAID-0 for gigantic
> transient files.  I do not anticipate using RAID for the system,
> partly because all bays are full.

Then you will need to add the new array UUIDs to the mdadm.conf file.

Since these will be non-system files for you I don't think you need
them in your initrd file.  The system will boot without it and will
start the arrays at normal boot time based upon the mdadm.conf file.
I think you can ignore the initrd part.

> > Mdadm has two different times when it will assemble raid volumes.  In
> > reverse time order the second is at boot time by looking at
> > /etc/mdadm/mdadm.conf file and assembling all raids configured there.
> > That data can be created using mdadm --scan to search for physical
> > devices and to produce the config files.  Take that information and
> > edit it as needed.

> Question: what is it that does this assembly at boot time?  Is there
> a daemon that's running now that I've installed mdadm?

After assembling the array there is a monitoring daemon that remains
to monitor the array.

> >   mdadm --detail --scan >>/dev/mdadm/mdadm.conf
> >   ...edit /dev/mdadm/mdadm.conf...clean up and remove duplicate lines...
>
> I might do the same, but you give no hint what that looks like, and I am not
> installing a new system to find out.

But you installed mdadm, right?  That will set up a default
/etc/mdadm/mdadm.conf file.  You have installed mdadm, right?  Simply
add to it.  Go look at your /etc/mdadm/mdadm.conf file and see what
format it is in.

The output of --scan would show something like this following.  So I
assume that is the minimum detail needed.

  # mdadm --examine --scan
  ARRAY /dev/md0 UUID=b83eb4b1:b3cd7664:92de4c59:171eb348
  ARRAY /dev/md1 UUID=b2dfa6c5:670c8ba1:9c78214e:3887479c
  ARRAY /dev/md2 UUID=c7c71eeb:ee54031a:bee4c713:8bfe3e2c
  ARRAY /dev/md3 UUID=a29d3855:f5821ceb:e683083b:09bfbf48

Also if you read the man page for mdadm it gives an example in the
documentation.  Although it is somewhat buggy and so I hesitate to
mention it.

But not to keep you in suspense I will include a full copy of the file
at the end of this message from one of my more active systems.  Along
with some gratuitous comments left behind because I think they give
some insight into working with this file as things are changed.  (I
would otherwise recommend a revision control system for /etc such as
supplied by the 'etckeeper' package.)

Bob

# mdadm.conf
#
# Please refer to mdadm.conf(5) for information about this file.
#

# by default, scan all partitions (/proc/partitions) for MD superblocks.
# alternatively, specify devices to scan, using wildcards if desired.
DEVICE partitions

# auto-create devices with Debian standard permissions
CREATE owner=root group=disk mode=0660 auto=yes

# automatically tag new arrays as belonging to the local system
HOMEHOST <system>

# instruct the monitoring daemon where to send mail alerts
MAILADDR root

# definitions of existing MD arrays
ARRAY /dev/md0 level=raid1 num-devices=2 UUID=f74177e1:a37e5f55:4b95c4af:47602a5c
ARRAY /dev/md1 level=raid1 num-devices=2 UUID=90c5bec9:93e14b15:c65e854d:a7b90415

# rwp: Added 2011-08-30
ARRAY /dev/md2 level=raid1 num-devices=2 UUID=4c31c5df:a1b27321:7a937297:90328cf8

# rwp: Removed 2012-10-09
# ARRAY /dev/md3 level=raid1 num-devices=2 UUID=3ef7c83d:6d36bf87:7a937297:90328cf8
# rwp: Added 2012-10-09
ARRAY /dev/md3 level=raid1 UUID=74d234d1:f9fc027f:7a937297:90328cf8
ARRAY /dev/md4 level=raid1 UUID=5d18b06d:4625b74b:7a937297:90328cf8


# This file was auto-generated on Fri, 12 Oct 2007 00:06:19 +0000
# by mkconf $Id: mkconf 261 2006-11-09 13:32:35Z madduck $

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