Hi, I haven't seen the issue come up on the btrfs mailing list recently, but in the year I've followed the list it has been fairly well established that the default kernel SCT is too short for desktop-class drives. I haven't personally run into issues, because my drives have 7sec SCT ERC, and the default kernel SCT is 30sec.
In addition to linking to this bug, I referenced the following thread on our wiki.d.o/btrfs page: https://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg53249.html In my opinion, smartmontools should not default to attempting to modify the SCT ERC of a drive. Instead it should query the drive's capabilities and only modify the kernel timeout if the query fails (assume desktop drive) or returns a large value (proof of desktop drive). From what I gather, that would be sufficient to close this bug. The second issue seems like it needs a new (normal priority) bug to be filed. That bug might be a request for a debconf interface to configure custom drive SCT ERC and kernel SCT values. I imagine a three column interface with device drive_SCT kernel_SCT columns would do the trick. This would be useful for following two cases: - tuning for greater performance (eg: read from redundant copy instead of waiting 7 sec, for more consistent IOPS) - allows drives with firmware preconfigured for RAID to be used in single disk volumes. Eg: if a user buys a "NAS" drive with 7sec SCT ERC, but wants maximum chance of recovery from read errors in single drive configuration, then the drive's firmware timeout should be reconfigured to something big like 120sec and the kernel SCT should be bumped to 180sec; this is the expected behaviour for single disk configuration. A long time ago I read that too low kernel SCT values are also a problem for ZFS, but of course the users who are hitting these problems are using "desktop" drives with crippled firmware for RAID. As I see it, this is an opportunity for Debian to distinguish itself as exemplary, because other distributions have not yet addressed these emerging issues. Of course, those "in the know" have already configured their systems correctly using rc.local... Sincerely, Nicholas
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