[CentOS] CentOS 4.4 lvm and drbd 0.8?

Sun Mar 4 15:44:25 UTC 2007
Ross S. W. Walker <rwalker at medallion.com>

> -----Original Message-----
> From: centos-bounces at centos.org 
> [mailto:centos-bounces at centos.org] On Behalf Of Johnny Hughes
> Sent: Sunday, March 04, 2007 7:16 AM
> To: CentOS ML
> Subject: Re: [CentOS] CentOS 4.4 lvm and drbd 0.8?
> On Fri, 2007-03-02 at 15:35 -0600, Les Mikesell wrote:
> > Johnny Hughes wrote:
> > > On Tue, 2007-02-27 at 00:20 -0600, Les Mikesell wrote:
> > >> Johnny Hughes wrote:
> > >>> I am not quite sure that drbd-8 is totally ready yet 
> for prime time.
> > >>> Not that I don't trust them (I use drbd in production 
> and I love it),
> > >>> but I want to wait for an 8.0.1 or 8.0.2 level before I move the
> > >>> enterprise CentOS RPMS to that version.
> > >>>
> > >>> I would be open to producing some 8.0.0 rpms for 
> testing ... though that
> > >>> will probably need to wait until after CentOS 5 Beta is 
> released.
> > >> Could you get the same effect by running software RAID1 
> with one of the 
> > >> drives connected via iscsi?
> > > 
> > > Provides the same effect as DRBD? ... not really ... as 
> DRBD provides a
> > > second machine in hot standby mode with a totally synced 
> partition that
> > > is ready to take over on a failure of the first machine.  
> If the first
> > > computer blows up (power supply, hard drive crash, etc.), 
> the second one
> > > starts up and takes over with no down time (except the 
> time it takes to
> > > mount the partition and start the services on the new machine).
> > 
> > How is the mirror/sync different than RAID1, and how is 
> DRBD's version
> > different than you would have if you exported the 2nd machine's 
> > partitions via iscsi and mirrored the live machine using md 
> devices with 
> > one local, one iscsi member for each?  If that is actually 
> possible, I'd 
> > expect those general purpose components too be much better 
> tested and 
> > more reliable than little-used code like DRBD.   Does DRBD 
> have special 
> > handling for updating slightly out-of-sync copies or does 
> it have to 
> > rebuild the whole thing if not taken down cleanly also?
> I have no idea how it works, other than it uses the md device 
> and raid 1
> kernel code to mirror the drive/partition to a second machine 
> ... and do
> so in real time.  It uses heartbeat to create a cluster and does real
> time failover.
> It does not require rebuilding the whole device if shutdown
> uncleanly ... it syncs from the last updated point.
> My point was that the 0.8 (actually renamed 8.0.0) code was just
> released.  The 0.6 and 0.7 code has been out and stable for quite
> sometime and I have been using it for more than 2 years.

If you were running a later kernel version of MD, it is conceivable
that you could create a mirror with a remote storage drive over

It would be up to you though to figure out how to fail-over to it
and to limit the bandwidth MD takes to that remote mirror and
releasize that it will always be fully synchronous and so
performance may not be the best over a WAN.

You can also use a pair of vise grip plyers to do the job of an
adjustable wrench, but it will probably strip the bolt in the


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