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From: Mikulas Patocka <mpatocka@redhat.com>
To: Paul Lawrence <paullawrence@google.com>
Cc: Alasdair Kergon <agk@redhat.com>,
	Mike Snitzer <snitzer@redhat.com>,
	linux-doc@vger.kernel.org, kernel-team@android.com,
	Jonathan Corbet <corbet@lwn.net>,
	linux-kernel@vger.kernel.org, dm-devel@redhat.com,
	Shaohua Li <shli@kernel.org>
Subject: Re: [dm-devel] [RFC] dm-bow working prototype
Date: Thu, 15 Nov 2018 18:15:34 -0500 (EST)	[thread overview]
Message-ID: <alpine.LRH.2.02.1811151809380.25860@file01.intranet.prod.int.rdu2.redhat.com> (raw)
In-Reply-To: <fba91b2e-4b2e-8daf-ff64-a12c9139cada@google.com>



On Mon, 29 Oct 2018, Paul Lawrence wrote:

> 
> > The snapshot target could be hacked so that it remembers space trimmed
> > with REQ_OP_DISCARD and won't reallocate these blocks.
> > 
> > But I suspect that running discard over the whole device would degrade
> > performance more than copying some unneeded data.
> > 
> > How much data do you intend to backup with this solution?
> > 
> > 
> We are space-constrained - we will have to free up space for the backup before
> we apply the update, so we have to predict the size and keeping usage as low
> as possible is thus very important.
> 
> Also, we've discussed the resizing requirement of the dm-snap solution and
> that part is not attractive at all - it seems it would be impossible to
> guarantee that the resizing happens in a timely fashion during the (very busy)
> update cycle.
> 
> Thanks everyone for the insights, especially into how dm-snap works, which I
> hadn't fully appreciated. At the moment, and for the above reasons, we intend
> to continue with the dm-bow solution, but do want to keep this discussion
> open. If anyone is going to be at Linux Plumbers, I'll be presenting this work
> and would love to chat about it more.

dm-snapshot took 9 years to fix the last data corruption bug (2004-2013 - 
the commit e9c6a182649f4259db704ae15a91ac820e63b0ca).

And with the new target duplicating the snapshot functionality, it may be 
the same.

Mikulas

  reply	other threads:[~2018-11-15 23:15 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-23 21:23 Paul Lawrence
2018-10-23 22:18 ` Alasdair G Kergon
2018-10-24 18:42   ` Paul Lawrence
2018-10-24 19:24     ` [dm-devel] " Mikulas Patocka
2018-10-25  0:01       ` Alasdair G Kergon
2018-10-25 10:20       ` Bryn M. Reeves
2018-10-25 17:23       ` Paul Lawrence
2018-10-26 20:03         ` Mikulas Patocka
2018-10-29 16:51           ` Paul Lawrence
2018-11-15 23:15             ` Mikulas Patocka [this message]
2018-12-02 10:07               ` Sandeep Patil
2018-10-25 16:30 ` MegaBrutal
2018-10-25 18:13   ` Paul Lawrence
2018-10-25 21:15     ` Wols Lists
2018-10-25 21:43 ` [dm-devel] " Darrick J. Wong

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