Interesting. Thanks for the additional information Andreas. On Tue, May 1, 2018 at 6:03 AM, Andreas Klauer <Andreas.Klauer@xxxxxxxxxxxxxx> wrote: > On Fri, Apr 27, 2018 at 09:32:08PM -0700, Nick Leli wrote: >> The RAID is utilized with LVM, but I would like to inspect the >> individual disks, to ensure that data is replicated in case of >> failure. > > You can run a RAID check and then see that mismatch_cnt is 0. > This should be enough to make sure all data is correct. > > If you don't trust the RAID system at all, and provided all > devices are using the same data offsets, you can use cmp. > > Setup: > > # truncate -s 100M a.img b.img > # losetup --find --show a.img > /dev/loop0 > # losetup --find --show b.img > /dev/loop1 > # mdadm --create /dev/md42 --level=1 --raid-devices=2 /dev/loop[01] > mdadm: Defaulting to version 1.2 metadata > mdadm: array /dev/md42 started. > # mkfs.ext4 /dev/md42 > # mkdir loop > # mount /dev/md42 loop/ > # echo Hello World > loop/HelloWorld.txt > # umount /dev/md42 > > Test: > > # cmp -l /dev/loop0 /dev/loop1 > 4257 0 1 > 4265 103 161 > 4266 210 64 > 4267 155 124 > 4268 313 203 > 4269 273 45 > 4270 154 216 > 4271 200 40 > 4272 351 206 > 4273 361 114 > 4274 264 262 > 4275 204 145 > 4276 21 204 > 4277 366 345 > 4278 140 144 > 4279 61 105 > 4280 126 265 > 4313 134 77 > 4314 53 372 > 4315 311 104 > 4316 264 333 > > So there are a few bytes difference, to be expected in metadata. > (device role 0 vs. device role 1, device UUID, checksum) > > If you don't want to compare metadata, you'd have to map out a > loop device with losetup --offset / --sizelimit that represents > actual data on the RAID itself. > > Checksums will only tell you that something is different, > not why and where (unless you do checksum per chunks of data). > > Note this will only work for 1:1 mirrored RAID modes. > > cmp would naturally complain about parity, or data offsets. > So for other RAID levels you have to rely on the built-in check > or use a tool that is aware of the specific RAID layout. > > Regards > Andreas Klauer -- 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
