[linux-lvm] Re: raid 1 on a single disk

ashwin chaugule ashwin.chaugule at gmail.com
Sun Nov 14 05:44:20 UTC 2004

There Greg ! , you got it right !
The media onto which the data will be stored is a small device, that
functions like a hdd,
this endeavour was just for a proof of concept.

I've also managed to hack into the kernel IDE susbsys. (ide-disk.c) to
duplicate the writes and reads for this particular disk.

So now I have two options for them.

RAID 1 is useful here (although its on one disk) because , data will
not be written / read _very_ often to/from the device. And in the
event that the media is flaky, will provide like a backup. The other
benefit is, I dont have to worry about the i/o errors (or any other
for that matter) while reading the contents back, the best copy
*should* be picked up by the md subsys itself.

However, in my driver (modified IDE) I have to take care of the writes
and reads individualy.
The advantage here is that, i dont need to make 4 partitions of the
disk, one is good enough, and the remaining can be unallocated. I make
the write at fixed offsets into the unallocated space, and when read
is requested, I read em one by one, and check.

So, there.

On Sat, 13 Nov 2004 17:00:35 -0500, Greg Freemyer
<greg.freemyer at gmail.com> wrote:
> >
> > P.S. I'd be really tempted to talk to the person asking you to do this, and ask them what they hope to achieve...
> > 
> I can almost envision times it would be useful.  i.e. disk speed is
> unimportand, disk data rarely changes, but when it does it is very
> important, and traditional backups are not feasible for some unknown
> reason?
> By having the data written to 2 different places on the disk, the
> likelyhood of a failure making it  truly unrecoverable is extremely
> small.
> ie. If you have disk media problems, likely only one location of the
> other will be affected.
> If you have a drive electronics failure, you can ship the drive off to
> have recovery performed.  (Over $1000 I know, but if the data is
> important.)
> Greg
> _______________________________________________
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> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

Ashwin Chaugule
Embedded Systems Engineer
Aftek Infosys ltd.
[Embedded Division]

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