From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Brown Subject: Re: Combining OCFS2 with Linux software RAID-0? Date: Fri, 11 Dec 2009 18:33:33 +1100 Message-ID: <20091211183333.09b48bbd@notabene.brown> References: <23986fd90912091503r3c671448va4d8637edfab472b@mail.gmail.com> <20091210123703.71b47ce7@notabene.brown> <20091211071526.GA4062@maude.comedia.it> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20091211071526.GA4062@maude.comedia.it> Sender: linux-raid-owner@vger.kernel.org To: Luca Berra Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On Fri, 11 Dec 2009 08:15:26 +0100 Luca Berra wrote: > On Thu, Dec 10, 2009 at 12:37:03PM +1100, Neil Brown wrote: > >On Wed, 9 Dec 2009 15:03:11 -0800 > >> Has anybody tried something like this? Are there alternative RAID-0 > >> solutions for Linux that would be expected to work? > > > >For RAID0 or LINEAR, this should work - give it a try. > > > _with_ a superblock? or without? Either. > what happens if one node modifies the superblock while the other is > running. Once a RAID0 has been created, there is never any need to modify the superblock, and I'm fairly sure we don't. > > >It might work for RAID1 one day to, but is unlikely to ever work for > >RAID5. > With an external metadata handler i believe it would be possible to > support up to raid1, maybe 10. That is the idea, yes. > > While in similar setups, data protection should be handled by the > storage system, raid 1 has its uses in a failover setup with two sites. > I don't see a real use for raid5/6 in such scenarios. If I had 16 nodes, each with a local device and a fast interconnect, I might want to have a filesystem that spanned all of the devices but survived the failure of any two nodes. Then having a stripe/parity layout across the devices would be useful. However I think the only way to get good performance would be to require that the filesystem does full-stripe writes every time. So I think that would look more like a clusterised ZFS ... but who knows. NeilBrown