• Tomasz Majchrzak's avatar
    raid1: prefer disk without bad blocks · d82dd0e3
    Tomasz Majchrzak authored
    If an array consists of two drives and the first drive has the bad
    block, the read request to the region overlapping the bad block chooses
    the same disk (with bad block) as device to read from over and over and
    the request gets stuck. If the first disk only partially overlaps with
    bad block, it becomes a candidate ("best disk") for shorter range of
    sectors. The second disk is capable of reading the entire requested
    range and it is updated accordingly, however it is not recorded as a
    best device for the request. In the end the request is sent to the first
    disk to read entire range of sectors. It fails and is re-tried in a
    moment but with the same outcome.
    
    Actually it is quite likely scenario but it had little exposure in my
    test until commit 715d40b93b10 ("md/raid1: add failfast handling for
    reads.") removed preference for idle disk. Such scenario had been
    passing as second disk was always chosen when idle.
    
    Reset a candidate ("best disk") to read from if disk can read entire
    range. Do it only if other disk has already been chosen as a candidate
    for a smaller range. The head position / disk type logic will select
    the best disk to read from - it is fine as disk with bad block won't be
    considered for it.
    Signed-off-by: default avatarTomasz Majchrzak <tomasz.majchrzak@intel.com>
    Signed-off-by: default avatarShaohua Li <shli@fb.com>
    d82dd0e3
raid1.c 91.3 KB