Network mirroring (was:R: Questions)

Marcelo Tosatti marcelo at
Tue Nov 2 21:48:02 MST 1999

On Tue, 2 Nov 1999 wanger at wrote:

> On Tue, 2 Nov 1999 09:29:21 -0200 (EDT), Marcelo Tosatti wrote: 
> >> 3. NBD (based on kernel RAID code)
> >NBD isnt based on RAID code. It allows you to use a remote block
> >device transparently. What you could for mirroring is adding a nbd device
> >as one of the devices on the RAID array. Someone tried this?
> Yes, I did some work with this.  The RAID code doesn't have a concept 
> of distributed file systems right now so it doesn't handle forcing 
> local reads but have global writes.  Also, it was quite unstable and 
> the reconstruct over 100Mbit was slow.  The GFS guys are working on 
> GNBD which will do these things correctly.  I believe they are also 
> doing the conversion to make nbd kernel code rather than the userland 
> stuff that is there now.
I know someone at NASA who wrote a GNBD kernel server but i didnt find the
code. Anyone has it? 

The thing to do now is in RAID. There is a draft or similar of "network
RAID" ? We could just do a hack into RAID to dont read from remote devices
(as you suggested) (someone already done that?) but wouldnt a new RAID
level optimized for network mirroring be better?

  - Marcelo


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