[Summary] How many replicas do I need for 2 drives?

From: hau tristan (cowby@dog.com)
Date: Thu Feb 24 2000 - 19:45:37 CST

Here are the summary:

1) 1 partition can store more than 1 replicas and in my case,
I only got 2 h/d and Sun Hotline told me that 3 replicas
should be stored in each partition say c0t1d0s7 and c0t8d0s7.
But if one of the mentioned partioions crash, the system will
still can boot up but in Single user mode.

2) It is not a perfect case and according to Jason Marshall:

       You want three or more replicas. If you lose 1/2 your replicas the
       will go into a "hard error" state. If you lose more than 1/2 your
       replicas the machine will panic. So, if you have three replicas on
       different disks, you can lose one of the disks without bad things
       happening to your volume (not important if you're using a stripe or
       concatenation without any redundancy, since if you lose a disk then,
       you're screwed anyway!).

3) mddb01 -c 3 /dev/dsk/c0t0d0s7 /dev/dsk/c0t8d0s7 is the right syntax
in md.tab.

   Thanks for all the mrgs :

Jason Marshall
arthur darren Dunham
Robert Hill
and many more who replied me.


< Org Post >

The doc. of ODS 4.0/4.1 suggested that "always have an odd # of
       3, 5, 7 etc ...)

       If my server only got 2 identical h/d :

       1) Do I still need 3 replicas ? 1 in c1 and 2 in c2 but in diff.
       partitions ?

       2) If 2 is okay for my setup. Will I face any setup problem e.g.
       ODS will
       not create even number of replicas.

       3) Is it the right syntax if 2 replicas is okay in md.tab ?

       mddb01 -c 2 /dev/dsk/c0t0d0s7 /dev/dsk/c0t1d0s7

       <more entries ....>


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