more mdadm questions

more mdadm questions

[rich turner]

when mdadm queries information about the raid devices, does it simply
get the imformation from /proc/mdstat and format it accordingly?

when mdadm displays information about the block devices raid devices are
built on how does it display the name the devices? does it show the
devfs name? does it show the mapper name if built on a logical volume?
are these names consistent?

what about raid devices that were built with raidtools? does it look in
/proc/mdstat for information?

how does mdadm know what devices to query if they are not defined in
/etc/mdadm/mdamd.conf with DEVICES?

if devices are missing from the raid device, is there a way of knowing
the name of the missing device without the configuration file?

Re: more mdadm questions

[maarten]

On Wednesday 01 September 2004 02:13, rich turner wrote:

Hi Rich,

Not wanting to be blunt an all...   but wouldn't most of these questions be 
answered by just running mdadm yourself...?

> when mdadm queries information about the raid devices, does it simply
> get the imformation from /proc/mdstat and format it accordingly?

My guess would be no, since /proc/mdstat gives less info than mdadm does.

> how does mdadm know what devices to query if they are not defined in
> /etc/mdadm/mdamd.conf with DEVICES?

Don't know how, but since 'mdadm --detail --scan' provides the info you can 
use to create the mdadm.conf file when missing, mdadm obviously does not rely 
on getting its info from that file at all. 

> if devices are missing from the raid device, is there a way of knowing
> the name of the missing device without the configuration file?

Yes.  Well, it depends on what you call "missing".  It will report a failed 
etc device, but if the array was created with a 'missing' drive it obviously 
cannot know what device will get added before you actually add it.

greetings,
Maarten

-- 

Re: more mdadm questions

[Neil Brown]

On Tuesday August 31, rich@storix.com wrote:
> when mdadm queries information about the raid devices, does it simply
> get the imformation from /proc/mdstat and format it accordingly?

It also used the GET_ARRAY_INFO and GET_DISK_INFO ioctls.
It also reads the super-block for more information.

> 
> when mdadm displays information about the block devices raid devices are
> built on how does it display the name the devices? does it show the
> devfs name? does it show the mapper name if built on a logical volume?
> are these names consistent?

It hunts through /dev for a special file with the name major/minor
numbers, and uses the name of the file.

> 
> what about raid devices that were built with raidtools? does it look in
> /proc/mdstat for information?

arrays built with raidtools are indistinguishable from arrays built
with mdadm.

> 
> how does mdadm know what devices to query if they are not defined in
> /etc/mdadm/mdamd.conf with DEVICES?

You must be using debian.  The conf file should be /etc/mdadm.conf,
and is most places.

I'm not sure what the question means.  "query" in what sense?
The only devices mdadm queries are those that it has been told to
query, possibly by /etc/mdadm.conf, possible by command line args.


> 
> if devices are missing from the raid device, is there a way of knowing
> the name of the missing device without the configuration file?

I'm not sure that question means anything.  If device is missing, then
it doesn't exist.  You can add a spare that will be rebuilt.  It can
be any un-used device of the right size.

Supposing there was a way of "knowing the name of the missing device",
how would you use that information?

NeilBrown