From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: reiser4 data journalling? Date: Sat, 30 Aug 2003 20:22:18 +0200 Message-ID: References: <3F4E3AF9.2060100@tupshin.com> <16206.16138.72832.920045@laputa.namesys.com> <3F4E6AA4.3030900@namesys.com> <20030829001814.GB9019@zero> <3F4E9C6D.2080009@namesys.com> <20030829012322.GJ21352@matchmail.com> <20030829050857.GA5755@namesys.com> <3F4F91DB.2080900@namesys.com> <16207.38985.871686.419166@laputa.namesys.com> <3F4FC8FD.1050303@namesys.com> Mime-Version: 1.0 Return-path: list-help: list-unsubscribe: list-post: Errors-To: flx@namesys.com In-Reply-To: <3F4FC8FD.1050303@namesys.com> (Hans Reiser's message of "Sat, 30 Aug 2003 01:43:25 +0400") List-Id: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Hans Reiser Cc: reiserfs-list@namesys.com Hans Reiser writes: >> > Because atomicity in ext3 basically consists of guaranteeing that the filesystem is consistent, and due to the disk drive implementation 4k blocks are written atomically. So, if you span more than one block, it is not guaranteed to be atomic. I was told most modern disks run with 32-64K blocks internally. 4K is very unlikely. Of course they don't always guarantee that a write of such a block is atomic, but then they also don't guarantee it for 4K. The only sure way is to wait for the disk telling you it is finished (= use write barriers) and/or turn the write buffer off. Even then you have to hope that the disk firmware doesn't lie to you. -Andi