From: Paul Lawrence <email@example.com> To: Mikulas Patocka <firstname.lastname@example.org> Cc: Alasdair Kergon <email@example.com>, Mike Snitzer <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org, Jonathan Corbet <email@example.com>, firstname.lastname@example.org, email@example.com, Shaohua Li <firstname.lastname@example.org> Subject: Re: [dm-devel] [RFC] dm-bow working prototype Date: Mon, 29 Oct 2018 09:51:48 -0700 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <alpine.LRH.firstname.lastname@example.org> > 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.
next prev parent reply other threads:[~2018-10-29 16:51 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 [this message] 2018-11-15 23:15 ` Mikulas Patocka 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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