On Wednesday 05 June 2013, Dave Howorth wrote:
Ruediger Meier wrote:
I'd benchmarked it and it's not faster for me. The advantage is that in case of inconsistencies you will get always the same data from one particular mirror.
I'd say that's a fairly unusual and worrying case.
Yes, but the probability to run into this case really high. That's why some people think that raid is completely useless at all.
Generally using both could be even slower if you have one fast and one slow HD.
Whilst true, I'd say that was also unusual and something to be avoided.
Anyway in my case I've noticed raid inconsistencies (without seeing any other problem) and I wanted to make two backups (one per mirror) without taking the raid offline.
Would it not be simpler just to copy from the underlying block devices?
I guess it would be a pain to get the lvm volumes running from /dev/sda and /dev/sdb instead of /dev/md2. And after doing this the raid mirrors would be even more inconsistent and moreover a pain to restore my current setup. How could it be simpler than this?: echo writemostly > /sys/devices/virtual/block/md2/md/dev-sda2/state dd if=/dev/system/vm06_root of=/tmp/vm06_root_sdb echo -writemostly > /sys/devices/virtual/block/md2/md/dev-sda2/state echo writemostly > /sys/devices/virtual/block/md2/md/dev-sdb2/state dd if=/dev/system/vm06_root of=/tmp/vm06_root_sda
Now I have such backups and I can diff and infestivate them further. $ md5sum /backup/kvm.0/* 03fb631ab6810e28bc23a4b700b36598 vm02_root_sda 51519c14d5dfed591fa5cd9dd4789b2f vm02_root_sdb 620e31b4bbf852e41413565f834a9a74 vm05_root_sda cd45de09ca60a2c058bb3a6fdc8cf5cc vm05_root_sdb 2592485256d561b2274b9525d63bbcb7 vm06_root_sda 5e5e04cbe82fb1971e8baa54c3485fe2 vm06_root_sdb 53f2dfdff8af2492006a97cbfeb1fc44 vm09_root_sda 53f2dfdff8af2492006a97cbfeb1fc44 vm09_root_sdb
There's something seriously wrong there. I wouldn't worry about taking the raid offline, because it looks like there's a major corruption problem so the data on it is extremely suspect!
Now I have everything to determine _exactly_ whether it's safe to repair it or not. For now it looks like I have luck. The inconsistencies came from a power failure some weeks ago and I can make it consistent again without serious problems and further downtime. cu, Rudi -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org