mdadm.conf unnecessary?

mdadm.conf unnecessary?

[Dexter Filmore]

What happens if I create two arrays and don't have an mdadm.conf file?

I ask because of this comment:

# mdadm will function properly without the use of a configuration file,
# but this file is useful for keeping track of arrays and member disks.

Um. so... that's all it does? Will mdadm -A -s gather all the info from.. from 
what?

Reason I ask: I have 8 sATA ports in the box with 4 disks that are going to 
replaced with 5 disks.

Now md0 currently is sd[abcd]1.
To copy data to the new array, I will have to build the new array degraded 
because I only have 8 ports.
So the new disks will be sd[efgh]1.
But when I pull the old drives after migrating, they will be sd[abcd]1.. so... 
how do I handle this?

Plus: how do I pass the "missing" disk on mdadm? /dev/sdi missing? After the 
old drives are out, it will become sde. but I can't pass sde as missing on 
creation, since at that point sde will be the first of the new drives.

Cross-eyed,

Dex


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Re: mdadm.conf unnecessary?

[Richard Scobie]

Dexter Filmore wrote:

> So the new disks will be sd[efgh]1.
> But when I pull the old drives after migrating, they will be sd[abcd]1.. so... 
> how do I handle this?

Make an mdadm.conf file that reflects your current array and use UUID's 
to identify the arrays - here is an example:

ARRAY /dev/md5 level=raid5 num-devices=4 
UUID=32cd6355:3c2c08a3:970a9f77:c13e51a3

Note, this should be all one line.

This will ensure that regardless of which /dev/sdX a drive is, the array 
will be assembled only from drives which are using this UUID.

mdadm -D /dev/mdX where X is your current array will give you the UUID 
of this array.

Regards,

Richard