echo *number* | sudo tee /sys/block/md0/md/stripe_cache_size
blockdev --setra *number* /dev/md0

For example:

echo 8192 > /sys/block/md0/md/stripe_cache_size
echo 256 > /sys/block/sdb/queue/max_sectors_kb
echo 256 > /sys/block/sdc/queue/max_sectors_kb
echo 256 > /sys/block/sdd/queue/max_sectors_kb
echo 256 > /sys/block/sde/queue/max_sectors_kb
blockdev --setra 64 /dev/sd[bcde]
blockdev --setra 16384 /dev/md0