[ENBD] raid1 mirroring inside enbd

[Peter T. Breuer]

"chacron1 wrote:"
> > > If i undertstand well this implementation enables mirroring of data block
> 
> I'll try to use it on a 2.14.18 . Is it easy to use ? Do i have to use specific
> partition type on disk ... ?

You need to have two server available (one may be on localhost) and use
a command line like:

> >   enbd-client piano:1044 -n 2 +xilophone:2022 -n 2  /dev/ndb
> >
> > (the -n 2 each time states  two channels in that "group" of channels).
> >
> > > > It's available in ftp://oboe.it.uc3m.es/pub/Programs/nbd-2.4.31.tgz .
> >
> > I haven't tested anything but the most basic things, such as the resync
> > shown above. I've decided to make the whole device resync if you do a
> > setfaulty, and to use the bitmap of notuptodate blocks if you do the
> > hotremove without the setfaulty.
> 
> Then , upon node failure enbd does a full resync and upon disk replacement
> a partial one .

This is being played with. The semantics changed again recently as a
result of conversations on this list. At the moment:


> >           echo 'setfaulty[b]=1' > /proc/nbdinfo

Starts the driver marking the bitmap on writes for group #1 of device
ndb.


> >            echo 'hotremove[b]=1' > /proc/nbdinfo


This (the above) marks the whole bitmap.

> >            echo 'hotadd[b]=1' > /proc/nbdinfo

This does the resync, as indicated by the bitmap, either full or
partial.


> > In addition, if the device drops out via a network fault, it will
> > be treated as though (2) above had occurred. When the network comes
> > back (3) will occur. Minor dropouts, such as losing a single channel
> > temporarily, are tolerated, as always.
> 
> What is your load balancing policy when several channel are available ?

It's demand balanced. If that means anything.


Peter