OT, but there seem to be a few people who understand such in-depth stuff here ;-)

I'm in the process of recovering (with ddrescue) files of a failing drive - no backups as "it's only TV" recordings and I can't afford the disk space anyway. It's going better than I expected with most of the files (typically anything between 1G and 4G in size) reading without any errors - retries on the disk, but no actual read errors.
Tedious because when the drive warms up, it "goes titsup*" (producing lots of DID_BAD_TARGET errors) and I have to unplug it and let it cool down before restarting the recovery process.

But, mounting the source drive read-only doesn't seem to actually mean read-only as I see errors in syslog related to write errors on the disk. After a dig around, I came across "blockdev --setro <device>" which as I read things means the device itself should be set as read-only.

But I still see things like this in syslog (when I unmount the filesystem) :
> end_request: I/O error, dev sdf, sector 3037143616
> Buffer I/O error on device sdf5, logical block 352878592
> lost page write due to I/O error on sdf5
> JBD2: Error -5 detected when updating journal superblock for sdf5-8.

Is it me not understanding things, or is it still trying to write to the disk ?
Or is it just that the filesystem code still tries to write, but fails either because the filesystem is mounted read-only or the device is set read-only ?


* Total Inability To Support Usual Performance