SUMMARY: Disksuite 4.2.1 replica/mirror problem

Managers,

Thanks for the comprehensive advice received from
- Darren Dunham,
- David Harrington,
- Rob De Langhe,
- Cris Lovett,
- Eric Ray,
- Tony Walsh.

All agreed that having a metadevice on the same slice as the state 
databases is not good practice, not in the least because it creates 
confusion for the ones who inherit such a set-up ;-).

To end the confusion (Q1): the databases share the same slice, but  are 
never included in the mirror. The metadevice simply skips the blocks 
used by the metadb's. We were therefore putting all our eggs in one 
basket and yes, in case of hardware failure on c0t0d0s6 the system would 
panic, crash and possibly become unbootable. There were no other 
databases on any other disk/slice, so SDS would refuse starting up as it 
would find less than 50% of its databases (0% to be sure!).

The consensus was to add databases on the A1000 (done), and to destroy 
the mirror (it was not mounted or used in any other way) and dedicate 
the seperate slices to meta-dbs. Which we will now do. A rule of thumb 
here seems to be: create at least 1 replica for each mirror in the 
set-up. The replicas should be distributed over at least 3 disks.

Q2: Breaking the (unused) mirror should not cause any problems, since 
the database blocks are not included in it. We will test this later 
today :0) .

Thanks,
Tony van Lingen (for Craig Robinson)


> -----Original Message-----
> From: Craig Robinson [mailto:craig.robinson@epa.qld.gov.au]
> Sent: Thursday, March 13, 2003 18:26
> To: Sunmanagers List (E-mail)
> Subject: Disksuite 4.2.1 replica/mirror problem
>
>
> Folks,
>
> We have inherited an E420R with 2 x internal 9.0Gb drives and a A1000
> attached.  The two internal drives are mirrored using Disksuite 
> 4.2.1.  One
> thing that I have noticed with this setup is that there are only 3 
> replicas on
> 1 slice (c0t0d0s6).  This slice is however mirrored on the second disk
> (c0t1d0s6).  Apart from the mirror, this gives us a single point of 
> failure if
> any of the disks go west.  I personally don't think the mirror would 
> save us,
> because it is the state database which actually informs us about the 
> mirror!!
>
> QUESTION 1:  If, for example, c0t0d0 failed would we get a panic OR 
> would the
> c0t1d0 mirror kick in?
>
> What we want to do is to break this mirror and create an extra replica 
> (i.e.
> having 2 x replicas on each disk).
>
> QUESTION 2: What would be the impact of breaking the mirror that the 
> state
> databases are on. Would we lose ALL disk information?
>
> Any comment would be appreciated. Will summarise.
>
> Cheers, Craig
> IT Technical Support
>
> Craig Robinson
> Environmental Protection Agency
> Tel: (07) 3006 4629     Fax: (07) 3227 6534
> Email: craig.robinson@epa.qld.gov.au
>
> Visit us at: http://www.epa.qld.gov.au
> _______________________________________________
> sunmanagers mailing list
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> http://www.sunmanagers.org/mailman/listinfo/sunmanagers
>

-- 
Tony van Lingen
Technical Consultant

Technology One Limited,
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