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Wed, 19 Nov 2025 08:59:33 -0800 (PST) Received: from [192.168.0.111] ([212.20.115.16]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-477aa387473sm44073645e9.4.2025.11.19.08.59.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 19 Nov 2025 08:59:33 -0800 (PST) Message-ID: <79169cc8-9166-4b65-9c59-d490512d46e6@redhat.com> Date: Wed, 19 Nov 2025 17:59:32 +0100 Precedence: bulk X-Mailing-List: linux-lvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: pvmove thin volume doesn't move To: "Brian J. Murrell" , linux-lvm@lists.linux.dev References: <1b6fb117-7283-4ba9-91ee-7412a2d77b3d@gmail.com> <29209080-c09b-40df-86c3-f22c1d7f6520@interlinx.bc.ca> <5067ec8d-991b-4b90-ad3b-f9dbbb0472d5@gmail.com> <81e51a5ad8f9c32610b8262447af635da81d53c3.camel@interlinx.bc.ca> <3620fc27-e54b-472d-bc82-be01f7b2739b@gmail.com> <6D706D06-AB0F-4C55-9F68-E8E07926A511@yahoo.com> <9c2a15d0-0d7d-4462-af43-83221c2ecbdd@gmail.com> <319f6df36c43e3c62e8edc9730e2d1f8065586ed.camel@interlinx.bc.ca> From: Zdenek Kabelac Organization: RedHat In-Reply-To: <319f6df36c43e3c62e8edc9730e2d1f8065586ed.camel@interlinx.bc.ca> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: ti2lOCqxEKS-MaqCeOTTogkNawCOnhcT61ghBJYxgCc_1763571576 X-Mimecast-Originator: redhat.com Content-Language: en-US, cs Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Dne 19. 11. 25 v 17:36 Brian J. Murrell napsal(a): >> lvm2  ATM does not support any sort of 'extraction' of a thinLV out >> of the >> thin-pool. > > Maybe that's an explanation that goes over my head with me not being an > LVM2 engineer but rather just a general jack-of-all-trades sysadmin. > > But that said, I'm not sure what kind of operation "extraction" is > supposed to be implying but I suppose what I was thinking (hoping for, > now it seems) was that in order to be able to move the blocks of an LV > in a thin-pool from one PV to another one would of course have to > extend the thin-pool to the new device, in the same way that any LV can > span devices. Ok - now I start to see - where we need to enhance our documentation. So here - 'adding' different space to thin-pool wouldn't not be a good idea. We will likely need to add at least 'prompt' protection if user would try to extend 'hdd' based LV used for thin-pool data with i.e. non-rotational (we are in planning phase for new allocation - which will be dealing with this - but we should add some protection to existing code base). thin-pool does it's own decision where it allocates 'chunks' for thin LV and for thin-pool itself given space is 'one big device' > >> As far as for documentation - I'm pretty sure we never mentioned any >> support >> of such operation within our lvm2 man pages. > > pvmove's manpage does describe the ability to move LVs among PVs. > That, IMO, implies thin-LVs without any kind of disclaimer saying > otherwise. > Ok - I'll try to add more details about 'virtual LVs' - which are thinLVs and vdoLVs (and we have even combination of both) Here we surely can add more disclaimers about the major difference between virtual and real LVs. >> Blocks in a standard LV are allocated (during creation) from the >> Volume Group >> (VG), but blocks in a thin LV  are  allocated  (during  use) >> from a "thin pool".  The thin pool contains blocks of physical >> storage, and >> thin LV blocks reference blocks in the thin pool. > > That sounds like a good description for an LVM2 software engineer > onboarding to thin provisioning. I don't think that description is > suitable to express the limitations (that are becoming apparent in this > thread) to general jack-of-all-trades system administrators as it > implies more knowledge of LVM2 than such a person could/would generally > have IMO. We surely always try to add the best details we can. But there is also some 'expectancy' user is somewhat knowledgeable. The performance of thin-pool ain't for free - so there are some drawbacks when user settles with thin-pools. > Again, much too technically detailed to express these limitations to a > general sysadmin that has to employ literally dozens of technologies in > one's administrative scope and therefore cannot possibly try understand > all of the underlying design decisions of every one of those dozens of > technologies. Like our error messaging - in case it makes no good explanation to the user should be always reported and requested for enhancement. Regards Zdenek