From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mr012msb.fastweb.it ([85.18.95.109]:54252 "EHLO mr012msb.fastweb.it" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754445AbdL1XT6 (ORCPT ); Thu, 28 Dec 2017 18:19:58 -0500 Received: from ceres.assyoma.it (93.63.55.57) by mr012msb.fastweb.it (5.8.043) id 5A415010004076E9 for linux-xfs@vger.kernel.org; Fri, 29 Dec 2017 00:14:14 +0100 Subject: Block size and read-modify-write MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Fri, 29 Dec 2017 00:14:14 +0100 From: Gionatan Danti Message-ID: <021d36d95a9de952ddd38cc56d18df4f@assyoma.it> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: linux-xfs@vger.kernel.org Cc: g.danti@assyoma.it Hi list, I would ask a question: how XFS block size affect read-modify-write in case of very small writes? For example, suppose an XFS filesystem with the default 4K data block size. Am I correct saying that: - a 512B normal, cached writes will cause a read-modify-write of the entire 4K sector? - a 512B O_DIRECT write will *not* cause a read-modify-write of the 4K sector, rather it will be flushed to disk as-is (512 bytes in length)? Thanks. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@assyoma.it - info@assyoma.it GPG public key ID: FF5F32A8