On 2018-04-15 21:04, Chris Murphy wrote:
I just ran into this:
https://github.com/neilbrown/mdadm/pull/32/commits/af1ddca7d5311dfc9ed60a5eb6497db1296f1bec

This solution is inadequate, can it be made more generic? This isn't
an md specific problem, it affects Btrfs and LVM as well. And in fact
raid0, and even none raid setups.

There is no good reason to prevent deep recovery, which is what
happens with the default command timer of 30 seconds, with this class
of drive. Basically that value is going to cause data loss for the
single device and also raid0 case, where the reset happens before deep
recovery has a chance. And even if deep recovery fails to return user
data, what we need to see is the proper error message: read error UNC,
rather than a link reset message which just obfuscates the problem.

This has been discussed at least once here before (probably more times, hard to be sure since it usually comes up as a side discussion in an only marginally related thread). Last I knew, the consensus here was that it needs to be changed upstream in the kernel, not by adding a udev rule because while the value is technically system policy, the default policy is brain-dead for anything but the original disks it was i9ntended for (30 seconds works perfectly fine for actual SCSI devices because they behave sanely in the face of media errors, but it's horribly inadequate for ATA devices).

To re-iterate what I've said before on the subject:

For ATA drives it should probably be 150 seconds. That's 30 seconds beyond the typical amount of time most consumer drives will keep retrying a sector, so even if it goes the full time to try and recover a sector this shouldn't trigger. The only people this change should negatively impact are those who have failing drives which support SCT ERC and have it enabled, but aren't already adjusting this timeout.

For physical SCSI devices, it should continue to be 30 seconds. SCSI disks are sensible here and don't waste your time trying to recover a sector. For PV-SCSI devices, it should probably be adjusted too, but I don't know what a reasonable value is.

For USB devices it should probably be higher than 30 seconds, but again I have no idea what a reasonable value is.

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