Re: AARGH! Please help. IDE controller fsckup

Re: AARGH! Please help. IDE controller fsckup

[Roy Sigurd Karlsbakk]

> > I have used presistent superblocks, but md0,1,2,3 will be differently
> > ordered if I change the disk order... At least I think so. It surely
> > didn't work.
>
> No. md0 would stay md0.  This is another effect of using superblocks,
> and in fact this is also (ironically) more or less the only argument
> *against* using them   :)
>
> (Imagine inserting a disk which knows that it is disk 0 of md0 into some
> machine that already has a perfectly fine md0 running)

ok. so. theoretically - as long as the system finds all 16 drives, I should be 
able to shuffle them around and attach them to whichever controller there is? 
right?

ok.

now, I've replaced the faulty controller, and booting up. the new controller 
is also (like the old one) a CMD649...

hæ?

it works. but it surely didn't work last time...

thanks

> > But ... with persistent superblock - is it possible to fsckup the raid?
>
> You're root, it is indeed possible  :)

er - yes. I more meant like 'automagically'

> But you would not need to perform any of the special operations that you
> need to now.
>
> Persistent superblocks saves you from a number of "bad" situations you
> can encounter with normal production systems (such as replacing a
> controller or moving disks around).
>
> One should be careful when moving disks with persistent superblocks
> between systems though. You don't want the kernel to autodetect the
> "wrong" md0 on boot   :)    I consider this problem nonexistent in the
> production environment that I administer, but I know that some people
> feel differently about it.  You should consider these pros and cons in
> relation to your environment and make a decision based on that.


-- 
Roy Sigurd Karlsbakk, Datavaktmester
ProntoTV AS - http://www.pronto.tv/
Tel: +47 9801 3356

Computers are like air conditioners.
They stop working when you open Windows.

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Re: AARGH! Please help. IDE controller fsckup

[Jakob Oestergaard]

On Thu, Oct 03, 2002 at 03:13:28PM +0200, Roy Sigurd Karlsbakk wrote:
> > > I have used presistent superblocks, but md0,1,2,3 will be differently
> > > ordered if I change the disk order... At least I think so. It surely
> > > didn't work.
> >
> > No. md0 would stay md0.  This is another effect of using superblocks,
> > and in fact this is also (ironically) more or less the only argument
> > *against* using them   :)
> >
> > (Imagine inserting a disk which knows that it is disk 0 of md0 into some
> > machine that already has a perfectly fine md0 running)
> 
> ok. so. theoretically - as long as the system finds all 16 drives, I should be 
> able to shuffle them around and attach them to whichever controller there is? 
> right?

It will not reattach your disks (you need to move cables to do that),
but it will know "First disk of md0" from "Second disk of md0"
regardless of whether those disks are /dev/hda or /dev/sdg.

You can shuffle your disks around as much as you please.  When the RAID
code looks at your disks, it will read their superblocks and correctly
make the first disk of md0 the first disk of md0, and so forth,
regardless of the actual device name of the disk.

> 
> ok.
> 
> now, I've replaced the faulty controller, and booting up. the new controller 
> is also (like the old one) a CMD649...
> 

RAID doesn't care about controllers.

RAID without persistent superblocks cares about disk device names.

RAID with persistent superblocks don't care about disk device names.

> hæ?

Øh?

> 
> it works. but it surely didn't work last time...
> 

Good for you  :)

> thanks
> 
> > > But ... with persistent superblock - is it possible to fsckup the raid?
> >
> > You're root, it is indeed possible  :)
> 
> er - yes. I more meant like 'automagically'

It will only automagically screw up your arrays if you shuffle disks
between machines (mix several RAID arrays from other systems in one
system)  (you can of course move all your disks to one new machine, if
it has none of it's original RAIDed disks left).

Just don't mix disks with persistent superblocks from multiple machines
into one single machine.  Unless you know exactly what you're doing.

-- 
................................................................
:   jakob@unthought.net   : And I see the elder races,         :
:.........................: putrid forms of man                :
:   Jakob Østergaard      : See him rise and claim the earth,  :
:        OZ9ABN           : his downfall is at hand.           :
:.........................:............{Konkhra}...............:
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Re: AARGH! Please help. IDE controller fsckup

[Andre Hedrick]

One of the observed issues under raid-tools is not looking at all the
devices' superblocks.  This would allow for out of order initialization.
Treating the devices as domino chips and stuffing them back in random
order and it working.

If I am wrong here, great.  Somebody please make the correction.

Cheers,

On Thu, 3 Oct 2002, Jakob Oestergaard wrote:

> On Thu, Oct 03, 2002 at 03:13:28PM +0200, Roy Sigurd Karlsbakk wrote:
> > > > I have used presistent superblocks, but md0,1,2,3 will be differently
> > > > ordered if I change the disk order... At least I think so. It surely
> > > > didn't work.
> > >
> > > No. md0 would stay md0.  This is another effect of using superblocks,
> > > and in fact this is also (ironically) more or less the only argument
> > > *against* using them   :)
> > >
> > > (Imagine inserting a disk which knows that it is disk 0 of md0 into some
> > > machine that already has a perfectly fine md0 running)
> > 
> > ok. so. theoretically - as long as the system finds all 16 drives, I should be 
> > able to shuffle them around and attach them to whichever controller there is? 
> > right?
> 
> It will not reattach your disks (you need to move cables to do that),
> but it will know "First disk of md0" from "Second disk of md0"
> regardless of whether those disks are /dev/hda or /dev/sdg.
> 
> You can shuffle your disks around as much as you please.  When the RAID
> code looks at your disks, it will read their superblocks and correctly
> make the first disk of md0 the first disk of md0, and so forth,
> regardless of the actual device name of the disk.
> 
> > 
> > ok.
> > 
> > now, I've replaced the faulty controller, and booting up. the new controller 
> > is also (like the old one) a CMD649...
> > 
> 
> RAID doesn't care about controllers.
> 
> RAID without persistent superblocks cares about disk device names.
> 
> RAID with persistent superblocks don't care about disk device names.
> 
> > hæ?
> 
> Øh?
> 
> > 
> > it works. but it surely didn't work last time...
> > 
> 
> Good for you  :)
> 
> > thanks
> > 
> > > > But ... with persistent superblock - is it possible to fsckup the raid?
> > >
> > > You're root, it is indeed possible  :)
> > 
> > er - yes. I more meant like 'automagically'
> 
> It will only automagically screw up your arrays if you shuffle disks
> between machines (mix several RAID arrays from other systems in one
> system)  (you can of course move all your disks to one new machine, if
> it has none of it's original RAIDed disks left).
> 
> Just don't mix disks with persistent superblocks from multiple machines
> into one single machine.  Unless you know exactly what you're doing.
> 
> -- 
> ................................................................
> :   jakob@unthought.net   : And I see the elder races,         :
> :.........................: putrid forms of man                :
> :   Jakob Østergaard      : See him rise and claim the earth,  :
> :        OZ9ABN           : his downfall is at hand.           :
> :.........................:............{Konkhra}...............:
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
> 

Andre Hedrick
LAD Storage Consulting Group

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Re: AARGH! Please help. IDE controller fsckup

[Jakob Oestergaard]

[snipping CC]

On Thu, Oct 03, 2002 at 01:05:44PM -0700, Andre Hedrick wrote:
> 
> One of the observed issues under raid-tools is not looking at all the
> devices' superblocks.  This would allow for out of order initialization.
> Treating the devices as domino chips and stuffing them back in random
> order and it working.

Have you seen this happening?  With non-development kernels?  ;)

There was one issue with raid startup that wouldn't start up arrays if
the first disk of the array was missing, or something like that. It was
a long-standing bug but it has been fixed.

I have not heard of the problem you're reporting.

> 
> If I am wrong here, great.  Somebody please make the correction.

Now is the time for someone out there to actually point out that error
which I blissfully ignored and which ruined their TB array of medical
records...   ;)

-- 
................................................................
:   jakob@unthought.net   : And I see the elder races,         :
:.........................: putrid forms of man                :
:   Jakob Østergaard      : See him rise and claim the earth,  :
:        OZ9ABN           : his downfall is at hand.           :
:.........................:............{Konkhra}...............:
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Re: AARGH! Please help. IDE controller fsckup

[Roy Sigurd Karlsbakk]

Jakob Oestergaard wrote:

>>>>But ... with persistent superblock - is it possible to fsckup the raid?
>>>>        
>>>>
>>>You're root, it is indeed possible  :)
>>>      
>>>
>>er - yes. I more meant like 'automagically'
>>    
>>
>
>It will only automagically screw up your arrays if you shuffle disks
>between machines (mix several RAID arrays from other systems in one
>system)  (you can of course move all your disks to one new machine, if
>it has none of it's original RAIDed disks left).
>
>Just don't mix disks with persistent superblocks from multiple machines
>into one single machine.  Unless you know exactly what you're doing.
>  
>
Could it be some kind of idea to 'sign' the disks with some hash out of 
hostname and  IP or something?

roy

Re: AARGH! Please help. IDE controller fsckup

[Adam Luter]

Just picking a severly large number at random would be good enough.
But more useful ideas would be to keep the first two or three blocks
over the n-disks as a md5 sum or other kind of checksum as your id.

Yeah, that means the id can change, but that's not very important... it
just needs to be unique so that the automagic stops if something weird
happens (an out of sync disk, or a foreign disk).

Or at least, this makes sense to me, with no prior sleep for 20 hours.

-Gryn (Adam Luter)

On Sat, Oct 05, 2002 at 05:42:07PM +0200, Roy Sigurd Karlsbakk wrote:
> >>>>But ... with persistent superblock - is it possible to fsckup the raid?
> >>>You're root, it is indeed possible  :)
> >>er - yes. I more meant like 'automagically'
> >
> >It will only automagically screw up your arrays if you shuffle disks
> >between machines (mix several RAID arrays from other systems in one
> >system)  (you can of course move all your disks to one new machine, if
> >it has none of it's original RAIDed disks left).
> >
> >Just don't mix disks with persistent superblocks from multiple machines
> >into one single machine.  Unless you know exactly what you're doing.
> >
> Could it be some kind of idea to 'sign' the disks with some hash out of 
> hostname and  IP or something?