From mboxrd@z Thu Jan 1 00:00:00 1970 References: <3f51904f43c45f8c1259f1b050402358@assyoma.it> <5070f4fa-81ad-9c9a-b0a7-8d5463ea09d3@redhat.com> <056d2d5dd9a7846a56971ce5f4cb3537@assyoma.it> From: Zdenek Kabelac Message-ID: <4f98430e-f6eb-b7b7-d1b0-f54ad07361de@redhat.com> Date: Thu, 17 Sep 2020 21:27:20 +0200 MIME-Version: 1.0 In-Reply-To: <056d2d5dd9a7846a56971ce5f4cb3537@assyoma.it> Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [linux-lvm] lvmcache with vdo - inconsistent block size Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: LVM general discussion and development , Gionatan Danti Dne 16. 09. 20 v 0:32 Gionatan Danti napsal(a): > Il 2020-09-15 20:34 Zdenek Kabelac ha scritto: >> Dne 14. 09. 20 v 23:44 Gionatan Danti napsal(a): >>> Hi all, >>> I am testing lvmcache with VDO and I have issue with devices block size. >>> >>> The big & slow VDO device is on top of a 4-disk MD RAID 10 device (itself >>> on top of dm-integrity). Over the VDO device I created a thinpool and a >>> thinvol [1]. When adding the cache device to the volume group via vgextend, >>> I get an error stating "Devices have inconsistent logical block sizes (4096 >>> and 512)." [2] >>> >>> Now, I know why the error shows and what i means. However, I don't know how >>> to force the cache device to act as a 4k sector device, and/if this is >>> really required to cache a VDO device. >>> >>> My current workaround is to set VDO with --emulate512=enabled, but this can >>> be suboptimal and it is not recommended. >>> >>> Any idea on what I am doing wrong? >> >> Hi >> >> LVM currently does not support mixing devices of different sector sizes within >> a single VG as it brings lot of troubles we have not yet clear vision what >> to do with all of them. > > Hi Zdenek, yes, I understand. What surprised me is that lvmvdo *can* be > combined with caching, and it does not suffer from this issue. Can you > elaborate on why it works in this case? > >> Also this combination of provisioned devices is not advised - since >> you are combining 2 kind of devices on top of each other and it can be >> a big problem >> to solve recovery case. > > True. > >> On lvm2 side we do not allow to use 'VDO LV' as backend for thin-pool device. > > I noticed it. However, from what I can read on RedHat docs, thinpool over VDO > device should be perfectly fine (the other way around, not so much). > You've most likely found the bug and this should be likely disable (and enabled only with some force option). Problem is, when such device stack is used for XFS - where the 'geometry' changes, but for some other it's not a big issue (i.e. ext4). So if you already hit some problem - feel free to open upstream BZ for this issue. Zdenek