Re: Mirroring and/or duplexing partitions

Lauri Tischler (
Sat, 6 Jul 1996 13:57:02 GMT +2

Anno Domini 5 Jul 96 at 20:44, Derrik Pates wrote:

> > Present incarnation of MD is neiter, it just gives you a large
> > diskspace without any redundancy.

> Not true, it provides EITHER linear append or RAID-0 striping (there's the
> mirroring). I'm not sure what the Duplexing thing is, however..

Sorry, but you are wrong.

LINEAR is just butting several disks one after the other, when one
fills up we begin to use the next one, no redundancy what so ever.

RAID-0, (striped) we use a bunch of disks as one big array, assume
three disks in an array and we write a file to it. Block 1 of file
goes to disk1, block 2 goes to disk2, block 3 goes to disk3, then we
start again.. block 4 goes to disk 1 ......
If You lose one disk ALL your data in GONE.
This is the reason why Raid Advisory Board does _not_ consired RAID-0
to be really part of RAID definition at all, _no redundancy_

RAID-1 (mirroring) You have two disks and same data is allways
written to both of them, if you lose one disk things still work.

This _mirroring_ is often called _duplexing_ when those disks are
on separate controllers.

There is also a thing called RAID-0/1 (also sometimes called RAID-6)
which means that you have two _striped arrays_ duplexed.

RAID-5 is parity controlled array.

Look for some info about this, it's a complicated thing :)

Lauri Tischler, Network Admin          Tel: +358-0-47846331 
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