-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 13/11/15 17:55, Gordon Messmer wrote: > On 11/13/2015 01:46 AM, J Martin Rushton wrote: >> If you really_need_ the guarantee of a snapshot, consider either >> LVM or RAID1. Break out a volume from the RAID set, back it up, >> then rebuild. > > FFS, don't do the latter. LVM is the standard filesystem backing > for Red Hat and CentOS systems, and fully supports consistent > snapshots without doing half-ass shit like breaking a RAID volume. > > Breaking a RAID volume doesn't make filesystems consistent, so when > you try to mount it, you might have a corrupt filesystem, or > corrupt data. Breaking the RAID will duplicate UUIDs of filesystems > and the name of volume groups. There are a whole bunch of > configurations where it just won't work. At best, it's unreliable. > Never do this. Don't advise other people to do it. Use LVM > snapshots (or ZFS if that's an option for you). > _______________________________________________ CentOS mailing > list CentOS at centos.org > https://lists.centos.org/mailman/listinfo/centos Maybe I should have been clearer: use (LVM) OR (RAID1 and break). Don't use LVM and break, that would be silly. I hope I'm wrong, but you wouldn't be thinking of mounting the broken out copy on a the same system would you? You must never do that, not even during disaster recovery. Use dd or similar on the disk, not the mounted partitions - isn't that obvious? I wasn't trying to give step by step instructions. Way before LVM existed we used this technique to back up VAXes (and later Alphas) under VMS using "volume shadowing" (ie RAID1). It worked quite happily for several years with disks shared across the cluster. IIRC it was actually recommended by DEC, indeed a selling point, but I don't have any manuals to hand to confirm that nowadays! One thing I did omit was you MUST sync first (there was an equivalent VMS command, don't ask me now), and also ensure that as the disks are added back a full catchup copy occurs. You may consider it half a mule's droppings, but it is, after all, what happens if you loose a spindle and hot replace. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) iQIcBAEBAgAGBQJWRk8fAAoJEAF3yXsqtyBlM50P/iHt5rwT/sGWSaNnsBNNoS0L WKb8Z9M7nVwaWsjceHPwEWMDrW2M7TUlXWCWhmDOL5oWP2PtX5J0YkXZ3ADmn5cp GE8gKmFDIdoepxs/GQREpryh+mT+kyhr+3WIISgSplEsGP0PezEBEX5jemvMAFcn bVH4KYj5Cqt/xludubqxaNe/GF72FwJKVl/ie5GIMF1gk039QpykOvI8GZzcXXVU /vEUH72i+JOgyrLCMIuzH6na2YSiXI1pav8NnPV4pZCX6Rre8/MTtNGRd8Lda3zR Nqb1Jow7ozTRwYWJpORU0ZiPN4aTQakktSLuPxN3KpAFOUiKbt4EMAI7YwceYh0b DwE7fml1auINn2XhwLYyHyX6bu0TJQmC8PbOxtx2J79wO0707ZPpvNN2imgGqYbg zdO7cQMlI04MqeRn9A+OgtLzAh/yrJaVDNYNN6OFbSpyfB0FrmrZpKxozX2gMOp2 C1WBffSflKN+RLAaWGsXY+CIDyHvkIJifUx+618O1iOqxXlWuMTmMa+Ez4DVpVLZ SIoQBmcE950ZE6mZZazdb2rGVC1OhQVcvsIxv3qDqxPUkBP5rrbYhW3SziqaOZHj M5o5iVkCRwBbxyV8GyVK8YYgBlu9CqxjMAfuNxT8aWZfl5kXVMxmfU8W2x4Pgjm1 n7ygIadGuw+cXEcr9ech =8SBu -----END PGP SIGNATURE-----