[DRBD-user] Any way to jump over initial sync ?

[David Bruzos]

Yeah, no problem.  Hopefully it helps you with 9.  It will be great if you update with DRBD9 specific details...

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David Bruzos (Systems Administrator)
Jacksonville Port Authority
2831 Talleyrand Ave.
Jacksonville, FL  32206
Cell: (904) 625-0969
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Email: david.bruzos at jaxport.com

On Wed, Aug 29, 2018 at 05:03:21PM +0200, Julien Escario wrote:
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> Many many thanks for the detailled procedure.
> 
> I'll try in a few days with drbd9 and will let you know if something has to be
> changed (mainly because resources are created on the fly on each side).
> 
> Julien
> 
> Le 29/08/2018 ?? 14:32, David Bruzos a ??crit :
> > Hi, I have lots of experience skipping the initial sync with ZFS zvols and 
> > drbd 8.4.x.  I have been using the "drbdadm -- --clear-bitmap 
> > new-current-uuid <RESOURCE>" for years and never had a problem.  This is 
> > why it works:
> > 
> > 1. New ZFS volumes are guaranteed to return only zero data for unwritten 
> > blocks, so two new volumes are always in sync, if they have not been 
> > written to. 2. Also, if you have a VM base image on two hosts, you can 
> > clone the volumes in the image on each host and also skip the initial
> > sync, because both clones will be identical.  Of course, I am asuming that
> > the base image was replicated via ZFS streams. 3. LVM volumes and most
> > other volume types will not work well, because they don't guarantee new
> > volumes to be zero-filled.  However, depending on your use case, it is
> > often better to zero-fill your volumes manually (E.G. cat /dev/zero
> > >/dev/vg/vol0) and skip the sync.  It does not seem reasonable, but given
> > the storage and network characteristics at play, it could be much much
> > better than doing an actual DRBD sync. 4. If in doubt, run a drbd verify
> > until you feel confidence in your process.
> > 
> > * Typical way to skip the sync (at least this is my proven method):
> > 
> > # drbdadm create-md <resource>  -  (do this on both nodes) # drbdadm up 
> > <resource>  -  (do this on both nodes) # drbdadm -- --clear-bitmap 
> > new-current-uuid <resource>  -  (do this on secondary node) # drbdadm 
> > primary <resource>  -  (do this on primary node) # cat /proc/drbd  - 
> > (Enjoy!)
> > 
> > In my opinion, having to replicate multi-tb volumes is an incredible waste 
> > of time and resources, if it can be safely avoided.  I've talked to many 
> > people that patiently wait while their giant 4 TB VM volumes do their 
> > initial sync and hog their environment's I/O in the process...
> > 
> > I hope this helps you and others out there who are looking for a better 
> > way...
> > 
> > David
> > 
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