• Keld Simonsen's avatar
    md: don't attempt read-balancing for raid10 'far' layouts · 8ed3a195
    Keld Simonsen authored
    This patch changes the disk to be read for layout "far > 1" to always be the
    disk with the lowest block address.
    
    Thus the chunks to be read will always be (for a fully functioning array) from
    the first band of stripes, and the raid will then work as a raid0 consisting
    of the first band of stripes.
    
    Some advantages:
    
    The fastest part which is the outer sectors of the disks involved will be
    used.  The outer blocks of a disk may be as much as 100 % faster than the
    inner blocks.
    
    Average seek time will be smaller, as seeks will always be confined to the
    first part of the disks.
    
    Mixed disks with different performance characteristics will work better, as
    they will work as raid0, the sequential read rate will be number of disks
    involved times the IO rate of the slowest disk.
    
    If a disk is malfunctioning, the first disk which is working, and has the
    lowest block address for the logical block will be used.
    Signed-off-by: default avatarKeld Simonsen <keld@dkuug.dk>
    Signed-off-by: default avatarNeil Brown <neilb@suse.de>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    8ed3a195
raid10.c 59.1 KB