On Tue, 30 Nov 2010 12:35:56 +0700 hansbkk@xxxxxxxxx wrote: > On Tue, Nov 30, 2010 at 7:42 AM, Neil Brown <neilb@xxxxxxx> wrote: > > If you are comparing recovering after some sort of problem with > > a RAID10 over 6 devices compared with LVM over 2 2-device RAID1s, then the > > former is certainly easier. This is simply because there are less layers of > > complexity where something could go wrong. > > > > In both cases, your data will be spread across multiple disks, and any one > > disk or even any two disks would be of no use to you. > > > Thanks Neil. > > Still true with LVM on top of the 6-drive set in either case? Yes. LVM will spread the data around in a different way, but it is still not possible to recovery anything reliably without all of the data. > > > Scenario being > All the drives are together and OK (generic SATA2, cleanly > disconnected) - but everything else is gone > Not practical to rebuild the whole set of hosts, just want to get at key data > Mount the disks on a new machine, boot from SystemRescueCD or Knoppix > and copy the key data off. There should be no difficulty doing that in either case. But there is more room for things to go wrong if you use LVM+MD than if you just use MD. So certainly use LVM if you need any of its features, but otherwise don't. > > > And between RAID6 and RAID10? I think this has already been answered. RAID10 tends to be faster, but with 5 or more devices, RAID6 makes more space available. RAID6 can survive any 2 devices failing. RAID10 over 6 devices can sometimes survive 3 failures, and sometimes not survive 2. NeilBrown > > > > On Mon, 29 Nov 2010 23:00:19 +0700 hansbkk@xxxxxxxxx wrote: > > > >> 2010/11/29 Keld Jørn Simonsen <keld@xxxxxxxxxx>: > >> >> I can see how RAID6 is simpler than RAID10, but compared to RAID1? > >> > > >> > Hmm, does not compute by me. RAID1 and RAID10 are the same in complexity, > >> > RAID10 is just a modern RAID1, and should actually have been called > >> > RAID1. > >> > >> My understanding is that if I use RAID10 on a single pair of disks > >> then that is literally the same as RAID1. These to me are very simple > >> in that I can take either one of the pair and mount it on any normal > >> machine and get at the data without doing anything special. > >> > >> However, if I have my six disks configured as a single RAID10 array, I > >> believe this is no longer true - the data from (at least the larger > >> of) the files has been distributed over all six disks, correct? > >> > >> Now compare putting LVM on top of this array, compared to three RAID1 > >> pairs on the one hand and a RAID6 array on the other (third) hand :) > >> > >> If I were trying to recover the data using the latest version of a > >> LiveCD - say Fedora or Knoppix, which would be easier? > >> > >> I'm not trying to score any points, it's a genuine question. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
