Re: [gentoo-user] Software RAID-1

[Peter Humphrey]

On Sunday 24 August 2014 19:22:40 Kerin Millar wrote:
> On 24/08/2014 14:51, Peter Humphrey wrote:
--->8
> > So I decided to clean up /etc/mdadm.conf by adding these lines:
> >
> > DEVICE /dev/sda* /dev/sdb*
> > ARRAY /dev/md5 devices=/dev/sda5,/dev/sdb5
> > ARRAY /dev/md7 devices=/dev/sda7,/dev/sdb7
> > ARRAY /dev/md9 devices=/dev/sda9,/dev/sdb9
>
> Perhaps you should not include /dev/md5 here.

I wondered about that.

> As you have made a point of building the array containing the root
> filesystem with 0.99 metadata, ...

...as was instructed in the howto at the time...

> I would assume that it is being assembled in kernelspace as a result of
> CONFIG_MD_AUTODETECT being enabled.

Yes, I think that's what's happening.

> Alternatively, perhaps you are using an initramfs.

Nope.

> Either way, by the time the mdraid init.d script executes, the /dev/md5
> array must - by definition - be up and mounted. Does it make a
> difference if you add the following line to the config?
>
>    AUTO +1.x homehost -all
>
> That will prevent it from considering arrays with 0.99 metadata.

No, I get the same result. Just a red asterisk at the left end of the line 
after "Starting up RAID devices..."

Now that I look at /etc/init.d/mdraid I see a few things that aren't quite 
kosher. The first is that it runs "mdadm -As 2>&1", which returns null after 
booting is finished (whence the empty line before the asterisk). Then it tests 
for the existence of /dev/md_d*. That also doesn't exist, though /dev/md* 
does:

# ls -l /dev/md*
brw-rw---- 1 root disk 9, 0 Aug 25 10:03 /dev/md0
brw-rw---- 1 root disk 9, 5 Aug 25 10:03 /dev/md5
brw-rw---- 1 root disk 9, 7 Aug 25 10:03 /dev/md7
brw-rw---- 1 root disk 9, 9 Aug 25 10:03 /dev/md9

/dev/md:
total 0
lrwxrwxrwx 1 root root 6 Aug 25 10:03 5_0 -> ../md5
lrwxrwxrwx 1 root root 6 Aug 25 10:03 7_0 -> ../md7
lrwxrwxrwx 1 root root 6 Aug 25 10:03 9_0 -> ../md9

Looks like I have some experimenting to do.

I forgot to mention in my first post that, on shutdown, when the script runs 
"mdadm -Ss 2>&1" I always get "Cannot get exclusive access to /dev/md5..." 
I've always just ignored it until now, but perhaps it's important?

> On a related note, despite upstream's efforts to make this as awkward as
> possible, it is possible to mimic the kernel's autodetect functionality
> in userspace with a config such as this:
>
>    HOMEHOST <ignore>
>    DEVICE partitions
>    AUTO +1.x -all
>
> Bear in mind that the mdraid script runs `mdadm --assemble --scan`.
> There is no need to specifically map out the properties of each array.
> This is what the metadata is for.

Thanks for the info, and the help. The fog is dispersing a bit...

-- 
Regards
Peter