On 20/09/19 17:24, Sarah Newman wrote: > On 9/20/19 8:59 AM, Wols Lists wrote: >> On 19/09/19 21:45, Liviu Petcu wrote: >>> Hello, >>> >>> Please let me know if in this situation detailed below, there are >>> chances of restoring the RAID 10 array and how I can do it safely. >>> Thank you! >> >> This is linux raid 10, not some form of raid 1+0? That's what it looks >> like to me. I notice it says the array is active! That I think is good >> news! > > I thought that there should be a flag like 'degraded' if the raid was > actually running. I can't find the kernel documentation any more. > >> >> Can you mount it read-only and read it? I would be surprised if you >> can't, which means the array is running fine in degraded mode. NOT GOOD >> but not a problem provided nothing further goes wrong. I notice it's >> also version 0.9 - is it an old array? Have the drives themselves >> failed? (which I guess is probably the case :-( I guess the drives >> effectively have just the one partition - 2 - and 1 is something >> unimportant? > > What you said is definitely true for a near layout for an even number of > devices and n=2. > > I thought the offset layout meant any two adjacent raid devices failing > was data loss, assuming this is accurate: > > http://www.ilsistemista.net/index.php/linux-a-unix/35-linux-software-raid-10-layouts-performance-near-far-and-offset-benchmark-analysis.html?start=1 > Except you've failed to extrapolate, sorry. We have six drives, not the four of the example. Although you could still be right. Does "offset=2" mean 2 copies, offset layout? The rule with raid-10 is that you can lose AT LEAST n-1 drives where n is the number of mirrors. So if there are three mirrors of two drives each, this array is safe. You can lose AT MOST p drives, where p is the number of drives in a mirror. So this array *could* be safe with 2 mirrors. What you can't do is lose n drives that are mirroring each other. The fact that the array is active makes me suspect that he is lucky. NOTE that mdadm has problems with a degraded array if it was working last time it tried! That doesn't mean it can't get it working, it means it's trying to draw attention to the problem. Cheers, Wol
