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[37.48.0.73]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-490bda4fd52sm292622755e9.0.2026.06.07.06.08.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 07 Jun 2026 06:08:42 -0700 (PDT) Message-ID: <20e7ea6e-1583-4274-a243-05e52f206a18@gmail.com> Date: Sun, 7 Jun 2026 15:08:41 +0200 Precedence: bulk X-Mailing-List: cryptsetup@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: dm-integrity: estimate the size needed for separate integrity device To: Max Gautier , cryptsetup@lists.linux.dev References: Content-Language: en-US Cc: Mikulas Patocka From: Milan Broz Autocrypt: addr=gmazyland@gmail.com; keydata= xsFNBE94p38BEADZRET8y1gVxlfDk44/XwBbFjC7eM6EanyCuivUPMmPwYDo9qRey0JdOGhW hAZeutGGxsKliozmeTL25Z6wWICu2oeY+ZfbgJQYHFeQ01NVwoYy57hhytZw/6IMLFRcIaWS Hd7oNdneQg6mVJcGdA/BOX68uo3RKSHj6Q8GoQ54F/NpCotzVcP1ORpVJ5ptyG0x6OZm5Esn 61pKE979wcHsz7EzcDYl+3MS63gZm+O3D1u80bUMmBUlxyEiC5jo5ksTFheA8m/5CAPQtxzY vgezYlLLS3nkxaq2ERK5DhvMv0NktXSutfWQsOI5WLjG7UWStwAnO2W+CVZLcnZV0K6OKDaF bCj4ovg5HV0FyQZknN2O5QbxesNlNWkMOJAnnX6c/zowO7jq8GCpa3oJl3xxmwFbCZtH4z3f EVw0wAFc2JlnufR4dhaax9fhNoUJ4OSVTi9zqstxhEyywkazakEvAYwOlC5+1FKoc9UIvApA GvgcTJGTOp7MuHptHGwWvGZEaJqcsqoy7rsYPxtDQ7bJuJJblzGIUxWAl8qsUsF8M4ISxBkf fcUYiR0wh1luUhXFo2rRTKT+Ic/nJDE66Ee4Ecn9+BPlNODhlEG1vk62rhiYSnyzy5MAUhUl stDxuEjYK+NGd2aYH0VANZalqlUZFTEdOdA6NYROxkYZVsVtXQARAQABzSBNaWxhbiBCcm96 IDxnbWF6eWxhbmRAZ21haWwuY29tPsLBlQQTAQgAPwIbAwYLCQgHAwIGFQgCCQoLBBYCAwEC HgECF4AWIQQqKRgkP95GZI0GhvnZsFd72T6Y/AUCYaUUZgUJJPhv5wAKCRDZsFd72T6Y/D5N D/438pkYd5NyycQ2Gu8YAjF57Od2GfeiftCDBOMXzh1XxIx7gLosLHvzCZ0SaRYPVF/Nr/X9 sreJVrMkwd1ILNdCQB1rLBhhKzwYFztmOYvdCG9LRrBVJPgtaYqO/0493CzXwQ7FfkEc4OVB uhBs4YwFu+kmhh0NngcP4jaaaIziHw/rQ9vLiAi28p1WeVTzOjtBt8QisTidS2VkZ+/iAgqB 9zz2UPkE1UXBAPU4iEsGCVXGWRz99IULsTNjP4K3p8ZpdZ6ovy7X6EN3lYhbpmXYLzZ3RXst PEojSvqpkSQsjUksR5VBE0GnaY4B8ZlM3Ng2o7vcxbToQOsOkbVGn+59rpBKgiRadRFuT+2D x80VrwWBccaph+VOfll9/4FVv+SBQ1wSPOUHl11TWVpdMFKtQgA5/HHldVqrcEssWJb9/tew 9pqxTDn6RHV/pfzKCspiiLVkI66BF802cpyboLBBSvcDuLHbOBHrpC+IXCZ7mgkCrgMlZMql wFWBjAu8Zlc5tQJPgE9eeQAQrfZRcLgux88PtxhVihA1OsMNoqYapgMzMTubLUMYCCsjrHZe nzw5uTcjig0RHz9ilMJlvVbhwVVLmmmf4p/R37QYaqm1RycLpvkUZUzSz2NCyTcZp9nM6ooR GhpDQWmUdH1Jz9T6E9//KIhI6xt4//P15ZfiIs7BTQRPeKd/ARAA3oR1fJ/D3GvnoInVqydD U9LGnMQaVSwQe+fjBy5/ILwo3pUZSVHdaKeVoa84gLO9g6JLToTo+ooMSBtsCkGHb//oiGTU 7KdLTLiFh6kmL6my11eiK53o1BI1CVwWMJ8jxbMBPet6exUubBzceBFbmqq3lVz4RZ2D1zKV njxB0/KjdbI53anIv7Ko1k+MwaKMTzO/O6vBmI71oGQkKO6WpcyzVjLIip9PEpDUYJRCrhKg hBeMPwe+AntP9Om4N/3AWF6icarGImnFvTYswR2Q+C6AoiAbqI4WmXOuzJLKiImwZrSYnSfQ 7qtdDGXWYr/N1+C+bgI8O6NuAg2cjFHE96xwJVhyaMzyROUZgm4qngaBvBvCQIhKzit61oBe I/drZ/d5JolzlKdZZrcmofmiCQRa+57OM3Fbl8ykFazN1ASyCex2UrftX5oHmhaeeRlGVaTV iEbAvU4PP4RnNKwaWQivsFhqQrfFFhvFV9CRSvsR6qu5eiFI6c8CjB49gBcKKAJ9a8gkyWs8 sg4PYY7L15XdRn8kOf/tg98UCM1vSBV2moEJA0f98/Z48LQXNb7dgvVRtH6owARspsV6nJyD vktsLTyMW5BW9q4NC1rgQC8GQXjrQ+iyQLNwy5ESe2MzGKkHogxKg4Pvi1wZh9Snr+RyB0Rq rIrzbXhyi47+7wcAEQEAAcLBfAQYAQgAJgIbDBYhBCopGCQ/3kZkjQaG+dmwV3vZPpj8BQJh pRSXBQkk+HAYAAoJENmwV3vZPpj8BPMP/iZV+XROOhs/MsKd7ngQeFgETkmt8YVhb2Rg3Vgp AQe9cn6aw9jk3CnB0ecNBdoyyt33t3vGNau6iCwlRfaTdXg9qtIyctuCQSewY2YMk5AS8Mmb XoGvjH1Z/irrVsoSz+N7HFPKIlAy8D/aRwS1CHm9saPQiGoeR/zThciVYncRG/U9J6sV8XH9 OEPnQQR4w/V1bYI9Sk+suGcSFN7pMRMsSslOma429A3bEbZ7Ikt9WTJnUY9XfL5ZqQnjLeRl 8243OTfuHSth26upjZIQ2esccZMYpQg0/MOlHvuFuFu6MFL/gZDNzH8jAcBrNd/6ABKsecYT nBInKH2TONc0kC65oAhrSSBNLudTuPHce/YBCsUCAEMwgJTybdpMQh9NkS68WxQtXxU6neoQ U7kEJGGFsc7/yXiQXuVvJUkK/Xs04X6j0l1f/6KLoNQ9ep/2In596B0BcvvaKv7gdDt1Trgg vlB+GpT+iFRLvhCBe5kAERREfRfmWJq1bHod/ulrp/VLGAaZlOBTgsCzufWF5SOLbZkmV2b5 xy2F/AU3oQUZncCvFMTWpBC+gO/o3kZCyyGCaQdQe4jS/FUJqR1suVwNMzcOJOP/LMQwujE/ Ch7XLM35VICo9qqhih4OvLHUAWzC5dNSipL+rSGHvWBdfXDhbezJIl6sp7/1rJfS8qPs In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi, On 6/1/26 9:50 AM, Max Gautier wrote: > I'm building a media server where I intend to use RAID10 on top of > dm-integrity (and cryptsetup on top of that, but that's not really > relevant, AFAIK). I plan to put the integrity tags of dm-integrity on my > NVME, to avoid some of the performance penalty. > > But I'm not sure what size each "integrity tags" partition should be, > depending on the data device. Interesting, while we can print information about data size, there is actually no calculation of size in the case of an independent data device. (And even this is post-format, we cannot calculate it in userspace in advance.) The only place for this is actually kernel dm-integrity, but the code is tricky. CC to Mikulas - is there a simple way to calculate this size? Or at least provide userspace with information about the existing meta device size (we send only the meta_device option as part of the mapping table). Actually, integritysetup should check device size before activation... (We have such a calculation for dm-verity for hash and FEC device, but not for dm-integrity.) Milan > > I'm using this blog [1] as the base for the calculation, but I couldn't > find a reference for the calculation in the dm-integrity kernel > documentation, in cryptsetup wiki or in the integritysetup man page. > > Is there a reference for calculating that size ? I'm fine looking at > some code, and it looks like the dm-integrity source[2] has some functions names > which could be helpful, but any pointers would help :) > > Thanks ! > > [1]: https://blog.tty8.org/posts/2025-04-02-moving-dm-integrity-tags-off-the-hdd-to-speed-up-raid.html > [2]: https://codebrowser.dev/linux/linux/drivers/md/dm-integrity.c.html >