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

[Lars Ellenberg <lars.ellenberg@linbit.com>]

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