From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from thunderbird6.fab.redhat.com (vpn-6-46.fab.redhat.com [10.33.6.46]) by ns3.rdu.redhat.com (8.13.8/8.13.8) with ESMTP id n3K86fIQ012708 for ; Mon, 20 Apr 2009 04:06:41 -0400 Message-ID: <49EC2C28.9030304@redhat.com> Date: Mon, 20 Apr 2009 09:02:48 +0100 From: "Bryn M. Reeves" MIME-Version: 1.0 Subject: Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"? References: <49DCA275.8070203@Calva.COM> <49DF02A7.50606@Calva.COM> <20090410101959.GA21846@us.ibm.com> <49DF2403.10009@Calva.COM> <49E32F57.8020105@redhat.com> <37d33d830904130730j6cb7bc16y50a2a6ac682dc5d@mail.gmail.com> In-Reply-To: <37d33d830904130730j6cb7bc16y50a2a6ac682dc5d@mail.gmail.com> Content-Transfer-Encoding: 7bit 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: Content-Type: text/plain; charset="us-ascii" To: LVM general discussion and development -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Sandeep K Sinha wrote: > On Mon, Apr 13, 2009 at 5:55 PM, Bryn M. Reeves wrote: > John Hughes wrote: >>>> malahal@us.ibm.com wrote: >>>>> John Hughes [john@Calva.COM] wrote: >>>>> >>>>>> John Hughes wrote: >>>>>> >>>>>>> if (lp->stripes > 1) { >>>>>>> log_error("mirrors and stripes are currently " >>>>>>> "incompatible"); >>>>>>> return 0; >>>>>>> } >>>>>>> >>>>>>> Should I just stick with mdadm for my mirroring and striping needs? >>>>>>> >>>>> You can do it today with some hassle or wait until someone implements a >>>>> feature called 'generic layering'. The feature really means, treat some >>>>> LVs as PVs! >>>>> >>>>> How can you do raid10 today? Create two raid0 LVs. Lets us call these >>>>> lvgroup0/lv0 and lvgroup0/lv1. Now create raid1 lv in lvgroup1 where >>>>> lvgroup1's PVs are lvgroup0/lv0 and lvgroup0/lv1. >>>>> >>>>> Isn't that a rai10 volume? > No, it's a RAID 0+1 (RAID01/mirror of stripes). > >>>> To increase the chances of surviving a double-disk failure it would be >>>> better to raid-0 a bunch of raid-1's. > This is RAID1+0 (RAID10/stripe of mirrors) - it's usually preferable to > 0+1 not only because of the improved redundancy but also the individual > >> I disagree. > >> Look at this: >> http://www.pcguide.com/ref/hdd/perf/raid/levels/multXY-c.html What do you disagree with? The article you linked to points out the same robustness and recovery concerns with a 0+1 layout as I mentioned earlier. It then goes on to say that this could be mitigated for 0+1 by a smart RAID implementation that continues to stripe to partially-failed RAID 0 sets but that most actual RAID controllers don't chose to implement this. The article seems to make the same claims as I did. Regards, Bryn. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org iEYEARECAAYFAknsLCgACgkQ6YSQoMYUY94KswCeOahyHLXilItIA8B1AR2Z/Ujb aloAn0jftWyKXqr9QK51tYkwmOWU68LF =mMPX -----END PGP SIGNATURE-----