linux-kernel - Re: [PATCH] drbd: Support zeroout device instead of initial full sync

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Message-ID: <20150818150319.GL19958@soda.linbit>
Date:	Tue, 18 Aug 2015 17:03:19 +0200
From:	Lars Ellenberg <lars.ellenberg@...bit.com>
To:	Nick Wang <nwang@...e.com>
Cc:	Philipp Reisner <philipp.reisner@...bit.com>,
	drbd-dev@...ts.linbit.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drbd: Support zeroout device instead of initial full sync

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

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