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Date: Tue, 18 Aug 2015 17:03:19 +0200
From: Lars Ellenberg <lars.ellenberg@linbit.com>
To: Nick Wang <nwang@suse.com>
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Cc: linux-kernel@vger.kernel.org, Philipp Reisner <philipp.reisner@linbit.com>,
	drbd-dev@lists.linbit.com
Subject: Re: [Drbd-dev] [PATCH] drbd: Support zeroout device instead of
	initial full sync
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On Thu, Aug 06, 2015 at 06:04:22PM +0800, Nick Wang wrote:
> Patch set for zeroing out device on both side
> instead of initial full sync. Useful for high
> latency network environment.
> 
> Implement --zeroout-devices and --discard-devices
> for new-current-uuid

I still think this does not belong into the kernel at all.
I may not yet have properly explained why.

This is a lot of stuff to add to the DRBD module,
introducing write protocol incompatibility/protocol version bump.

For no good reason.

you want to create a new drbd,
and want to make sure the backing devices are discarded:

# blkdiscard /dev/backing
and then proceed with
# drbdadm create-md ...
as normal, and skip the initial sync as documented.

You want to grow an existing drbd,
you have to grow the backend first, anyways,
you can then (if necessary)
# blkdiscard --offset $o --length $l /dev/backing,
# drbdadm resize ... --assume-clean ...

No need to touch either the DRBD module, or the DRBD utils at all.
All there already.

	Lars Ellenberg