there are upper and lower limits (32768, 16). Default is 128.
strip_cache_active (currently raid5 only)
number of active entries in the stripe cache
+ preread_bypass_threshold (currently raid5 only)
+ number of times a stripe requiring preread will be bypassed by
+ a stripe that does not require preread. For fairness defaults
+ to 1. Setting this to 0 disables bypass accounting and
+ requires preread stripes to wait until all full-width stripe-
+ writes are complete. Valid values are 0 to stripe_cache_size.