from raidtools2 to mdadm

from raidtools2 to mdadm

[Clemens Schwaighofer]

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Hi,

as debian changed their package from raidtools2 to mdadm and left us
users out in the cold (no mdadm.conf craeted, lsraid commands left in
crontab, etc), I am now a bit worried if the command

#> mdadm --detail --scan>> mdadm.conf

is enought to get the raid started the next time I have to reboot the box.

Until now I used only the raidtools (raidhotadd, lsraid, etc). Is there
somehwere a reference like what raidhotadd would be in mdadm command?

-- 
[ Clemens Schwaighofer                      -----=====:::::~ ]
[ TEQUILA\ Japan IT Group                                    ]
[                6-17-2 Ginza Chuo-ku, Tokyo 104-8167, JAPAN ]
[ Tel: +81-(0)3-3545-7703            Fax: +81-(0)3-3545-7343 ]
[ http://www.tequila.co.jp                                   ]

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Re: from raidtools2 to mdadm

[Neil Brown]

On Tuesday June 21, cs@tequila.co.jp wrote:
> Hi,
> 
> as debian changed their package from raidtools2 to mdadm and left us
> users out in the cold (no mdadm.conf craeted, lsraid commands left in
> crontab, etc), I am now a bit worried if the command

Unfortunate...

> 
> #> mdadm --detail --scan>> mdadm.conf
> 
> is enought to get the raid started the next time I have to reboot
> the box.

1/ remove the 'devices=' parts.  Then it should be ok, providing there
   is a suitable DEVICES line at the top.
2/ If you were depending on 'raidstart' to start your arrays before,
   mdadm will definitely be more reliable (which is to say that it
   should still work if you lose the first drive of your array...)
3/ Best way to find out is to try it!

> 
> Until now I used only the raidtools (raidhotadd, lsraid, etc). Is there
> somehwere a reference like what raidhotadd would be in mdadm
> command?

Well, there is the man-page for mdadm.  An understanding is always
better than a cheat-sheet...

But raidhotadd /dev/mdX /dev/hdY  -> mdaddm /dev/mdX --add /dev/hdy
    s/add/remove/
    raidstop -> mdadm --stop

There is no real equivalent for mkraid. mdadm --create does the same
thing in a very different way.

NeilBrown

Re: from raidtools2 to mdadm

[Clemens Schwaighofer]

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On 06/21/2005 02:54 PM, Neil Brown wrote:

>>#> mdadm --detail --scan>> mdadm.conf
>>
>>is enought to get the raid started the next time I have to reboot
>>the box.
> 
> 
> 1/ remove the 'devices=' parts.  Then it should be ok, providing there
>    is a suitable DEVICES line at the top.

yeah I have a devices line on the top. If I don't have, I will need the
devices lines I guess.

> 2/ If you were depending on 'raidstart' to start your arrays before,
>    mdadm will definitely be more reliable (which is to say that it
>    should still work if you lose the first drive of your array...)

no, it should be now called via the mdadm start

> 3/ Best way to find out is to try it!

well :) not if you have production boxes with sw raid :D

>>Until now I used only the raidtools (raidhotadd, lsraid, etc). Is there
>>somehwere a reference like what raidhotadd would be in mdadm
>>command?
> 
> 
> Well, there is the man-page for mdadm.  An understanding is always
> better than a cheat-sheet...

yeah, I am crawling through the docs, and man pages to get a thinking of it.

> But raidhotadd /dev/mdX /dev/hdY  -> mdaddm /dev/mdX --add /dev/hdy
>     s/add/remove/
>     raidstop -> mdadm --stop
> 
> There is no real equivalent for mkraid. mdadm --create does the same
> thing in a very different way.

yeah, but I more often have to add/remove a device than I have to create
a new raid, so its fine :)


-- 
[ Clemens Schwaighofer                      -----=====:::::~ ]
[ TEQUILA\ Japan IT Group                                    ]
[                6-17-2 Ginza Chuo-ku, Tokyo 104-8167, JAPAN ]
[ Tel: +81-(0)3-3545-7703            Fax: +81-(0)3-3545-7343 ]
[ http://www.tequila.co.jp                                   ]

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Re: from raidtools2 to mdadm

[Neil Brown]

On Tuesday June 21, cs@tequila.co.jp wrote:
> On 06/21/2005 02:54 PM, Neil Brown wrote:
> 
> >>#> mdadm --detail --scan>> mdadm.conf
> >>
> >>is enought to get the raid started the next time I have to reboot
> >>the box.
> > 
> > 
> > 1/ remove the 'devices=' parts.  Then it should be ok, providing there
> >    is a suitable DEVICES line at the top.
> 
> yeah I have a devices line on the top. If I don't have, I will need the
> devices lines I guess.

No..
The 'devices=' bits by themselves aren't enough, and are rarely
wanted.
If a device isn't listed in the DEVICES lines, then it won't be
considered for use in an array.

The 'devices=' words are quite different.  They say "this is how you
recognise a device that is in this array.  All the devices in it are
on this list".
This is reported by "mdadm --detail --scan" largely for interest.  It
should rarely be included in mdadm.conf.  The very latest version ofn
mdadm does not report them unless --verbose is given.

NeilBrown

Re: from raidtools2 to mdadm

[Clemens Schwaighofer]

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On 06/21/2005 03:25 PM, Neil Brown wrote:

> No..
> The 'devices=' bits by themselves aren't enough, and are rarely
> wanted.
> If a device isn't listed in the DEVICES lines, then it won't be
> considered for use in an array.

okay

> The 'devices=' words are quite different.  They say "this is how you
> recognise a device that is in this array.  All the devices in it are
> on this list".
> This is reported by "mdadm --detail --scan" largely for interest.  It
> should rarely be included in mdadm.conf.  The very latest version ofn
> mdadm does not report them unless --verbose is given.

okay, then I have an old one, because mine gives it to me, thats why I
had it in my conf file.

thanks for all the help

-- 
[ Clemens Schwaighofer                      -----=====:::::~ ]
[ TEQUILA\ Japan IT Group                                    ]
[                6-17-2 Ginza Chuo-ku, Tokyo 104-8167, JAPAN ]
[ Tel: +81-(0)3-3545-7703            Fax: +81-(0)3-3545-7343 ]
[ http://www.tequila.co.jp                                   ]

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Re: from raidtools2 to mdadm

[Bill Davidsen]

Neil Brown wrote:

>On Tuesday June 21, cs@tequila.co.jp wrote:
>  
>
>>On 06/21/2005 02:54 PM, Neil Brown wrote:
>>
>>    
>>
>>>>#> mdadm --detail --scan>> mdadm.conf
>>>>
>>>>is enought to get the raid started the next time I have to reboot
>>>>the box.
>>>>        
>>>>
>>>1/ remove the 'devices=' parts.  Then it should be ok, providing there
>>>   is a suitable DEVICES line at the top.
>>>      
>>>
>>yeah I have a devices line on the top. If I don't have, I will need the
>>devices lines I guess.
>>    
>>
>
>No..
>The 'devices=' bits by themselves aren't enough, and are rarely
>wanted.
>If a device isn't listed in the DEVICES lines, then it won't be
>considered for use in an array.
>
>The 'devices=' words are quite different.  They say "this is how you
>recognise a device that is in this array.  All the devices in it are
>on this list".
>This is reported by "mdadm --detail --scan" largely for interest.  It
>should rarely be included in mdadm.conf.  The very latest version ofn
>mdadm does not report them unless --verbose is given.
>

So is there no way to ask mdadm to take what's running and create a 
config to make it happen again? Telling people to cread the man pages 
for a utility they did not use by choice and create a config file which 
could result in losing their data if it's wrong is a deterent to an 
upgrade, I suspect.

It would be desirable to follow the example of iptables, to allow rules 
to be configured by hand (more or less) and then have a tool to create a 
config file from what's there. A human readable editable file at that.

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979

Re: from raidtools2 to mdadm

[Neil Brown]

On Wednesday June 22, davidsen@tmr.com wrote:
> 
> So is there no way to ask mdadm to take what's running and create a 
> config to make it happen again? Telling people to cread the man pages 
> for a utility they did not use by choice and create a config file which 
> could result in losing their data if it's wrong is a deterent to an 
> upgrade, I suspect.

There is a complexity in that devices can change there names across
reboot, and mdadm has no way to know a minimal set of possible new
names.

You could:
  echo DEVICES partitions > /etc/mdadm.conf
  mdadm -Ds | grep -v devices >> /etc/mdadm.conf

and then
  mdadm -As

should re-assemble  everything properly at boot time.
However this might not handle stacked devices (raid0 comprised for
raid1s) very well (maybe an enhancement for the next mdadm?).

A bad config file is unlikely to cause data loss.  It might result it
data not being visible until the problem is fixed.

I'm working towards making auto-assembly more bullet-proof, but it is
not trivial, and I would rather it not give the appearance of working
correctly until it really does (in contrast to 'raidstart' which gives
the appearance of working correctly until a drive fails.  Then it
fails too :-( )

NeilBrown

Re: from raidtools2 to mdadm

[Luca Berra]

On Tue, Jun 21, 2005 at 02:40:54PM +0900, Clemens Schwaighofer wrote:
>Hi,
>
>as debian changed their package from raidtools2 to mdadm and left us
>users out in the cold (no mdadm.conf craeted, lsraid commands left in
>crontab, etc), I am now a bit worried if the command
>
>#> mdadm --detail --scan>> mdadm.conf
>
i use this script to convert from old raidtab to mdadm.con
http://cvs.mandriva.com/cgi-bin/cvsweb.cgi/SPECS/mdadm/raidtabtomdadm.sh



-- 
Luca Berra -- bluca@comedia.it
        Communication Media & Services S.r.l.
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