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Old 05-11-2014, 10:25 PM   #1
telemeister
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RAID + MDADM + LILO Questions: Slackware 14.1


I have a machine which was at Slackware 13.0, and have had to replace some
hardware. I am taking the opportunity to upgrade to Slackware 14.1 64 bit.
The behaviour of RAID+MDADM+LILO seems a bit different than before.

Basically I am using software RAID-1 on all partitions.

I wonder if someone experienced can confirm a couple of things:

Q1. It looks like in order to use LILO I need to do the mdadm --create
with metadata=0.90, rather than the default (metadata=1.2). Is this correct?


I did this on the root partition, and now LILO works. Also it seems that when the machine boots it correctly identifies that raid array as /dev/md0 as I defined it. All the other partitions (created using the default metadata=1.2) are booting as md125, md124 etc (rather than the names I used when I created them).


Q2. Is there any downside to just creating all the raid arrays using metadata=0.90, so that I get the expected names?

Q3. If there is a downside to metadata=0.90, can someone outline the correct way to force the raid arrays to boot with known names?

Thanks - appreciate any input or pointers to links.
Steve
 
Old 05-11-2014, 10:36 PM   #2
Richard Cranium
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I'm willing to bet that if you start reading here, you will see why your array names are wrong.

It's not the metadata format, it's the contents of /etc/mdadm.conf in your initrd.
 
Old 05-12-2014, 07:32 PM   #3
telemeister
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Thanks very much for the link, which I had read previously.
This did effectively answer my third question and is one way to get it working.

My other questions were aimed at understanding things a bit better.

1. Can someone confirm that if you want to use LILO you need to use "mdadm --create --metadata=0.90" for
the root partition?

2. Contrary to your comment, the metadata format must have some influence on the array naming. If you use metadata=0.90 the array naming is always correct without any need to adjust the mdadm.conf file.

So the question was: Is there a downside to using mdadm with metadata=0.90 for all partitions
(since I have to use it on the root partition anyway.)?

Appreciate any input.

Steve
 
Old 05-12-2014, 07:56 PM   #4
TracyTiger
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Quote:
Originally Posted by telemeister View Post
1. Can someone confirm that if you want to use LILO you need to use "mdadm --create --metadata=0.90" for
the root partition?
Version 0.90 is required (by LILO) for the partition containing /boot. It's not required for other partitions.

If /boot is a separate partition then the root partition does NOT have to use a version 0.90 superblock format.

EDIT: Regarding your question # 2, you may find the following from the man page interesting.
Code:
       -e, --metadata=
              Declare the style of RAID metadata (superblock) to be used.  The
              default  is 1.2 for --create, and to guess for other operations.
              The default can be overridden by setting the metadata value  for
              the CREATE keyword in mdadm.conf.

              Options are:

              0, 0.90
                     Use  the  original  0.90  format superblock.  This format
                     limits arrays to 28 component devices and  limits  compo-
                     nent  devices of levels 1 and greater to 2 terabytes.  It
                     is also possible for there to be confusion about  whether
                     the superblock applies to a whole device or just the last
                     partition, if that partition starts on a 64K boundary.

              1, 1.0, 1.1, 1.2 default
                     Use the new version-1 format superblock.  This has  fewer
                     restrictions.   It can easily be moved between hosts with
                     different endian-ness, and a recovery  operation  can  be
                     checkpointed  and  restarted.  The different sub-versions
                     store  the  superblock  at  different  locations  on  the
                     device,  either  at  the end (for 1.0), at the start (for
                     1.1) or 4K from the start (for 1.2).  "1"  is  equivalent
                     to  "1.2" (the commonly preferred 1.x format).  "default"
                     is equivalent to "1.2".
The advise given in this forum about software RAID usually comes from experience of what works and what may not work, rather than a complete understanding of how it works. The functioning of RAID has changed some over the last couple of years and we've been struggling some to figure out what works.

EDIT2: If you just want it to work follow the instruction in post # 44 in the link provided by Richard Cranium in post # 2 of this thread. He spent time figuring it all out.

Last edited by TracyTiger; 05-12-2014 at 08:44 PM.
 
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Old 05-12-2014, 08:52 PM   #5
telemeister
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Thanks v. much Richard Cranium and TracyTiger for those links and answers.

All clear now.

Steve
 
Old 05-13-2014, 09:13 AM   #6
Richard Cranium
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Quote:
Originally Posted by telemeister View Post
2. Contrary to your comment, the metadata format must have some influence on the array naming. If you use metadata=0.90 the array naming is always correct without any need to adjust the mdadm.conf file.
Ahh. A little more googling and I found this thread over in Gentoo land.

If you are using the 0.90 metadata format, the kernel auto-assembles the raid devices for you (unless you turn that off). When udevd kicks off during init, it will attempt to assemble any other arrays for you using /lib/udev/rules.d/64-md-raid.rules.

Quote:
So the question was: Is there a downside to using mdadm with metadata=0.90 for all partitions
(since I have to use it on the root partition anyway.)?
There's this.
 
  


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