From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zdenek Kabelac Subject: Re: [RFC] zodcache - auto-start dm-cache devices Date: Fri, 18 Dec 2015 22:06:32 +0100 Message-ID: <56747558.7030507@redhat.com> References: <20151218185110.GA25064@agk-dp.fab.redhat.com> <56747182.2030404@gmail.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <56747182.2030404@gmail.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: device-mapper development List-Id: dm-devel.ids Dne 18.12.2015 v 21:50 Ian Pilcher napsal(a): > On 12/18/2015 12:51 PM, Alasdair G Kergon wrote: >> Did you try stacking LVM on top of itself first? > > Honestly, no (although my initial testing of zodcache actually used > logical volumes as the origin and cache devices FWIW). > > This exercise is as much about the "optics" as it is about the actual > technical merits of the solution. The goal is provide something that > (at least on the surface) looks "simple". > > With just a couple of obvious enhancements to the mkzc utility (clear > the metadata region and start the new device), creating a cached device > would literally take just a single command. > Sure - as long as you do not need to solve any 'security/safety' points, you can do things in a simple way. But how do you plan to support any power-failures and recoveries ? When someone pick drive to other system - what is going to happen ? Are you going to write your own 'lvm2-like' tools to do the job ? Are you going to maintain this over long time period ? You really should have started from RFE on lvm2 enhancements to better suite your needs - since IMHO there are no SIMPLE things when we talk about devices... Regards Zdenek