Tang, > There is a machine with very little max_sectors_kb size: > [root@ceph151 queue]# pwd > /sys/block/sdd/queue > [root@ceph151 queue]# cat max_hw_sectors_kb > 256 > [root@ceph151 queue]# cat max_sectors_kb > 256 > > The performance is very low when I run big I/Os. > I can not modify it directly, I need a little bigger, > so how can I enlarge it?
max_hw_sectors_kb is set based on the DMA transfer capabilities of the SCSI controller. max_sectors_kb is a soft limit for regular filesystem I/O. It can not exceed max_hw_sectors_kb since that would violate the hardware constraints. You need to figure out why your controller is limiting the transfer size. -- Martin K. Petersen Oracle Linux Engineering
