The problem is due to a common misconfiguration. Consumer drives have longer recoveries potentially, upwards of minutes, trying to recover a flaky sector. The OS sees this as an unresponsive drive, and eventually does a link reset. This is 30 seconds by default on Linux, not sure about others. The link reset prevents the drive from reporting an explicit read error along with the affected sector LBA. That information is needed for RAID to know what data to rebuild from parity, send that up to the app layer, and also send a good copy back to the sector that reported the read error. So eventually there's an accumulation of these, and in case of a drive failure and another drive that produces a URE, poof, imploded array. Now, you can recover from this, sorta, but it's tedious and requires a sort of skill to do it. So most people give up. Ergo RAID is not a backup. Backup your RAIDs. And make sure drive SCT ERC is shorter than the kernel's SCSI/ATA command timer. Ideally shorten the drive timeout. If that can't be done (consumer drive) then increase the kernel's command timer. Both of these are per device settings.