Merge branch 'master' into from-stable

[thirdparty/mdadm.git] / md.4

diff --git a/md.4 b/md.4
index dfd287f1f156db44c03715fa26303c0b6f6c9011..ea12eaffaf1570f040801ff518c5a62b4b655d12 100644 (file)
--- a/md.4
+++ b/md.4
@@ -526,10 +526,22 @@ Finally, "idle" can be written to stop the check/repair process.
 .B md/stripe_cache_size
 This is only available on RAID5 and RAID6.  It records the size (in
 pages per device) of the  stripe cache which is used for synchronising
-all read and write operations to the array.  The default is 128.
+all write operations to the array and all read operations if the array
+is degraded.  The default is 256.  Valid values are 17 to 32768.
 Increasing this number can increase performance in some situations, at
-some cost in system memory.
+some cost in system memory.  Note, setting this value too high can
+result in an "out of memory" condition for the system.
 
+memory_consumed = system_page_size * nr_disks * stripe_cache_size
+
+.TP
+.B md/preread_bypass_threshold
+This is only available on RAID5 and RAID6.  This variable sets the
+number of times MD will service a full-stripe-write before servicing a
+stripe that requires some "prereading".  For fairness this defaults to
+1.  Valid values are 0 to stripe_cache_size.  Setting this to 0
+maximizes sequential-write throughput at the cost of fairness to threads
+doing small or random writes.  
 
 .SS KERNEL PARAMETERS