dracut: qestions about mdraid module

Hello,

I'm looking at the module 'mdraid' of dracut (0.38) and was wondering the purpose of rd.md.uuid= parameter.

I understand it can be used to selectively activate the array matching the UUID passed through the parameter but I'm wondering in which cases it can be useful...

Also I don't really understand why dracut try to do its own mechanism to achieve that (by providing its own udev rules which are modified at boot time) whereas mdadm already provide the infrastructure (through mdadm.conf) in a cleaner way (IMHO).

Another question, hopefully you don't mind: dracut provide an udev set of rules in a file named 59-persistent-storage-md.rules. I still don't really see the point since most of the stuff in it seems to already be done by the rule fileudev-md-raid-arrays.rules, shipped by mdadm (3.3.2).

Ah my last question not related to mdraid: why dracut uses stderr to print out all its messages: info, debug, error. Stderr is usually used for error/warning messages only.

Thanks !

Quoted 5 lines · Francis Moreau

Hello,

I'm looking at the module 'mdraid' of dracut (0.38) and was wondering the purpose of rd.md.uuid= parameter.

Quoted 8 lines

I understand it can be used to selectively activate the array matching the UUID passed through the parameter but I'm wondering in which cases it can be useful...

Also I don't really understand why dracut try to do its own mechanism to achieve that (by providing its own udev rules which are modified at boot time) whereas mdadm already provide the infrastructure (through mdadm.conf) in a cleaner way (IMHO).

If mdadm.conf is not included in the initramfs, you want to have a way to prevent automatic assembly of all raids found. With big machines, lots of disk, you only want to assemble those, which you really need.

Quoted 5 lines

Another question, hopefully you don't mind: dracut provide an udev set of rules in a file named 59-persistent-storage-md.rules. I still don't really see the point since most of the stuff in it seems to already be done by the rule fileudev-md-raid-arrays.rules, shipped by mdadm (3.3.2).

That wasn't always the case in all distributions. Nowadays can probably be removed.

Quoted 6 lines

Ah my last question not related to mdraid: why dracut uses stderr to print out all its messages: info, debug, error. Stderr is usually used for error/warning messages only.

Thanks !

Hmm, not true.

    warn() {
        echo "Warning: $*" >&2
    }

    info() {
        echo "$*"
    }

see.. warn() goes to error, info() to stdout.

This is in the initramfs, though.
Or do you mean dracut the tool?

Quoted 16 lines · Francis Moreau

Quoted 5 lines

Hello,

I'm looking at the module 'mdraid' of dracut (0.38) and was wondering the purpose of rd.md.uuid= parameter.

Quoted 8 lines

I understand it can be used to selectively activate the array matching the UUID passed through the parameter but I'm wondering in which cases it can be useful...

Also I don't really understand why dracut try to do its own mechanism to achieve that (by providing its own udev rules which are modified at boot time) whereas mdadm already provide the infrastructure (through mdadm.conf) in a cleaner way (IMHO).

Quoted 4 lines

If mdadm.conf is not included in the initramfs, you want to have a way to prevent automatic assembly of all raids found. With big machines, lots of disk, you only want to assemble those, which you really need.

Ok but why mdadm.conf wouldn't be included in the initramfs ? If one doesn't want to start all arrays during the boot process, it's very likely he doesn't start all arrays automatically while the system is running, no ?