From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Williams Subject: Re: [PATCH 1/4] md: Factor out RAID6 algorithms into lib/ Date: Sat, 18 Jul 2009 09:26:16 -0700 Message-ID: References: <1247494302.19180.268.camel@macbook.infradead.org> <4A5F6590.9000006@zytor.com> <4A608913.1060808@redhat.com> <4A6096A0.5050501@zytor.com> <4A609A52.7070506@redhat.com> <4A609B72.2010901@zytor.com> <4A609CFA.2060707@redhat.com> <4A609D8D.8050501@zytor.com> <1247918016.22313.138.camel@macbook.infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: "H. Peter Anvin" , Ric Wheeler , chris.mason@oracle.com, linux-btrfs@vger.kernel.org, neilb@suse.de, linux-raid@vger.kernel.org To: David Woodhouse Return-path: In-Reply-To: <1247918016.22313.138.camel@macbook.infradead.org> List-ID: On Sat, Jul 18, 2009 at 4:53 AM, David Woodhouse w= rote: > On Fri, 2009-07-17 at 11:49 -0400, H. Peter Anvin wrote: >> Cost, yes, of changing an on-disk format. > > Personally, I don't care about that -- I'm utterly uninterested in th= e > legacy RAID-6 setup where it pretends to be a normal disk. I think th= at > model is as fundamentally wrong as flash devices making the similar > pretence. I can understand the frustration of these details being irretrievably hidden behind a proprietary interface out of the filesystem's control. However, this is not the case with Linux software RAID. I suspect that there is room for more interaction with even "legacy" filesystems to communicate things like: "don't worry about initializing that region of the disk it's all free space", "don't bother resyncing on dirty shutdown, if power-loss interrupts a write I guarantee I will replay the entire stripe to you at a later date", or "hey, that last block I read doesn't checksum, can you come up with a different version?" I was under the impression that btrfs wanted to leverage md's stripe handling logic as well, seems that is not the case? -- Dan > =B9 Well, kind of. The xor_blocks() function will silently screw you = over > =A0if you ask it to handle more than 5 blocks at a time. async_xor() handles arbitrary block counts. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" = in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html