On 11/24/20 11:05 AM, Simon Matter wrote:
On 11/24/20 1:20 AM, Simon Matter wrote:
On 23/11/2020 17:16, Ralf Prengel wrote:
Backup!!!!!!!!
Von meinem iPhone gesendet
You do have a recent backup available anyway, haven't you? That is: Even without planning to replace disks. And testing such strategies/sequences using loopback devices is definitely a good idea to get used to the machinery...
On a side note: I have had a fair number of drives die on me during RAID-rebuild so I would try to avoid (if at all possible) to deliberately reduce redundancy just for a drive swap. I have never had a problem (yet) due to a problem with the RAID-1 kernel code itself. And: If you have to change a disk because it already has issues it may be dangerous to do a backup - especially if you do a file based backups
because the random access pattern may make things worse. Been there, done that...
Sure, and for large disks I even go further: don't put the whole disk into one RAID device but build multiple segments, like create 6 partitions of same size on each disk and build six RAID1s out of it.
Oh, boy, what a mess this will create! I have inherited a machine which was set up by someone with software RAID like that. You need to replace one drive, other RAIDs which that drive's other partitions are participating are affected too.
Now imagine that somehow at some moment you have several RAIDs each of them is not redundant, but in each it is partition from different drive that is kicked out. And now you are stuck unable to remove any of failed drives, removal of each will trash one or another RAID (which are not redundant already). I guess the guy who left me with this setup listened to advises like the one you just gave. What a pain it is to deal with any drive failure on this machine!!
It is known since forever: The most robust setup is the simplest one.
I understand that, I also like keeping things simple (KISS).
Now, in my own experience, with these multi terabyte drives today, in 95% of the cases where you get a problem it is with a single block which can not be read fine. A single write to the sector makes the drive remap it and problem is solved. That's where a simple resync of the affected RAID segment is the fix. If a drive happens to produce such a condition once a year, there is absolutely no reason to replace the drive, just trigger the remapping of the bad sector and and drive will remember it in the internal bad sector map. This happens all the time without giving an error to the OS level, as long as the drive could still read and reconstruct the correct data.
In the 5% of cases where a drive really fails completely and needs replacement, you have to resync the 10 RAID segments, yes. I usually do it with a small script and it doesn't take more than some minutes.
It is one story if you administer one home server. It is quite different is you administer a couple of hundreds of them, like I do. And just 2-3 machines set up in such a disastrous manner as I just described suck 10-20 times more of my time each compared to any other machine - the ones I configured hardware for myself, and set up myself, then you are entitled to say what I said.
Your assumptions about my work environment are quite wrong.
Hence the attitude.
Keep things simple, so they do not suck your time - if you do it for living.
But if it is a hobby of yours - the one that takes all your time, and gives you a pleasure just to fiddle with it, then it's your time, and your pleasure, do it the way to get more of it ;-)
It was a hobby 35 years ago coding in assembler and designing PCBs for computer extensions.
Simon