From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx1.redhat.com (ext-mx20.extmail.prod.ext.phx2.redhat.com [10.5.110.49]) by smtp.corp.redhat.com (Postfix) with ESMTPS id ED7A75DE5B for ; Wed, 23 Oct 2019 12:12:56 +0000 (UTC) Received: from mail.service4.ru (mail.service4.ru [95.217.67.65]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A12B03086246 for ; Wed, 23 Oct 2019 12:12:53 +0000 (UTC) Received: from mail.service4.ru (localhost [127.0.0.1]) by mail.service4.ru (Postfix) with ESMTP id 0F9AC40962 for ; Wed, 23 Oct 2019 15:12:52 +0300 (MSK) Received: from mail.service4.ru ([127.0.0.1]) by mail.service4.ru (mail.service4.ru [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id ct591czGFMVq for ; Wed, 23 Oct 2019 15:12:51 +0300 (MSK) Received: from ilia (unknown [95.217.67.1]) by mail.service4.ru (Postfix) with ESMTPSA id 3F12540310 for ; Wed, 23 Oct 2019 15:12:51 +0300 (MSK) References: <909d4cae-ddd2-3951-eee8-8dec8faa6f22@redhat.com> From: Ilia Zykov Message-ID: <4daf9dc2-c2b4-7191-80c4-fa2073d7b5e9@service4.ru> Date: Wed, 23 Oct 2019 15:12:52 +0300 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256; boundary="------------ms020701070205010904000503" Subject: Re: [linux-lvm] exposing snapshot block device 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: To: linux-lvm@redhat.com This is a cryptographically signed message in MIME format. --------------ms020701070205010904000503 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 23.10.2019 14:08, Gionatan Danti wrote: >=20 > For example, consider a completely filled 64k chunk thin volume (with > thinpool having ample free space). Snapshotting it and writing a 4k > block on origin will obviously cause a read of the original 64k chunk, > an in-memory change of the 4k block and a write of the entire modified > 64k block to a new location. But writing, say, a 1 MB block should *not= * > cause the same read on source: after all, the read data will be > immediately discarded, overwritten by the changed 1 MB block. >=20 > However, my testing shows that source chunks are always read, even when= > completely overwritten. Not only read but sometimes write. I watched it without snapshot. Only zeroing was enabled. Before wrote new chunks "dd bs=3D1048576 ..." chunks were zeroed. But for security it'= s good. IMHO: In this case best choice firstly write chunks to the disk and then give this chunks to the volume. >=20 > Am I missing something? >=20 --------------ms020701070205010904000503 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCC C5gwggVJMIIEMaADAgECAhB4cYLFWiS6TlQZt1XHO6t8MA0GCSqGSIb3DQEBCwUAMIGCMQsw CQYDVQQGEwJJVDEPMA0GA1UECAwGTWlsYW5vMQ8wDQYDVQQHDAZNaWxhbm8xIzAhBgNVBAoM GkFjdGFsaXMgUy5wLkEuLzAzMzU4NTIwOTY3MSwwKgYDVQQDDCNBY3RhbGlzIENsaWVudCBB dXRoZW50aWNhdGlvbiBDQSBHMTAeFw0xOTA4MTUxMzIzMjhaFw0yMDA4MTUxMzIzMjhaMBsx GTAXBgNVBAMMEG1haWxAc2VydmljZTQucnUwggEiMA0GCSqGSIb3DQEBAQUAA4IBDwAwggEK AoIBAQCVtIsFGaETpCy13RrPlkkWnljEyXpI9AXCaVqXgwJ1Zw6rnUndl3FPB6L7e4tnaT2w OAXak0cbxS4AlUOXfYA6cSfS42n5QUOdo7HKoS+F50hYeiwXetF6q2UejDcdTXQsXLwXyk3d 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