On 10 Feb 2019, Harald Dunkel spake thusly: > On 1/27/19 12:21 AM, Nik.Brt. wrote: >> >> These mismatches happen, in raid1, but why they happen is not precisely known. There are a few ideas... and it is said that they are harmless in most cases (=outside of files). >> The phenomenon happens a lot less if you have LVM over the raid1, and also this is not exactly known why. > > This is more than alarming. Do I put my data at risk using software RAID1? No, because the only situation in which they are known to happen is when you have a powerdown or crash or similar event when the data has hit one spindle and not the other. In this case, *either* content is valid: if you get one, you could have got the other if the machine powered down a fraction of a second earlier or later. All that matters is that the data remains conssitent. RAID is not meant to protect against data loss on sudden powerdown (that's the job of UPSes and filesystem journals) nor really against data loss on single-sector disk damage or intemittent connectivity problems. It's meant to protect against data loss on whole-disk failure. That's all. If it protects against other things, good, but other scenarios are not within the design intent of RAID. -- NULL && (void)
