On 10/5/23 15:36, Dave Chinner wrote:
$ lspci |grep -i nvme 03:00.0 Non-Volatile memory controller: Samsung Electronics Co Ltd NVMe SSD Controller SM981/PM981/PM983 06:00.0 Non-Volatile memory controller: Samsung Electronics Co Ltd NVMe SSD Controller SM981/PM981/PM983 $ cat /sys/block/nvme*n1/queue/write_cache write back write back $ That they have volatile writeback caches....
It seems like what I wrote has been misunderstood completely. With "handling a power failure cleanly" I meant that power cycling a block device does not result in read errors nor in reading data that has never been written. Although it is hard to find information about this topic, here is what I found online: * About certain SSDs with power loss protection: https://us.transcend-info.com/embedded/technology/power-loss-protection-plp * About another class of SSDs with power loss protection: https://www.kingston.com/en/blog/servers-and-data-centers/ssd-power-loss-protection * About yet another class of SSDs with power loss protection: https://phisonblog.com/avoiding-ssd-data-loss-with-phisons-power-loss-protection-2/ So far I haven't found any information about hard disks and power failure handling. What I found is that most current hard disks protect data with ECC. The ECC mechanism should provide good protection against reading data that has never been written. If a power failure occurs while a hard disk is writing a physical block, can this result in a read error after power is restored? If so, is this behavior allowed by storage standards? Bart.
