Assemble: allow members of containers to be assembled and auto-assembled.

[thirdparty/mdadm.git] / md.4

diff --git a/md.4 b/md.4
index db39aba66584c46051198c499b64c89deb173e43..ea12eaffaf1570f040801ff518c5a62b4b655d12 100644 (file)
--- a/md.4
+++ b/md.4
@@ -1,9 +1,9 @@
-''' Copyright Neil Brown and others.
-'''   This program is free software; you can redistribute it and/or modify
-'''   it under the terms of the GNU General Public License as published by
-'''   the Free Software Foundation; either version 2 of the License, or
-'''   (at your option) any later version.
-''' See file COPYING in distribution for details.
+.\" Copyright Neil Brown and others.
+.\"   This program is free software; you can redistribute it and/or modify
+.\"   it under the terms of the GNU General Public License as published by
+.\"   the Free Software Foundation; either version 2 of the License, or
+.\"   (at your option) any later version.
+.\" See file COPYING in distribution for details.
 .TH MD 4
 .SH NAME
 md \- Multiple Device driver aka Linux Software RAID
@@ -16,8 +16,8 @@ The
 .B md
 driver provides virtual devices that are created from one or more
 independent underlying devices.  This array of devices often contains
-redundancy, and hence the acronym RAID which stands for a Redundant
-Array of Independent Devices.
+redundancy and the devices are often disk drives, hence the acronym RAID
+which stands for a Redundant Array of Independent Disks.
 .PP
 .B md
 supports RAID levels
@@ -240,7 +240,7 @@ across a later section of all drives, always ensuring that all copies
 of any given block are on different drives.
 
 The 'far' arrangement can give sequential read performance equal to
-that of a RAID0 array, but at the cost of degraded write performance.
+that of a RAID0 array, but at the cost of reduced write performance.
 
 When 'offset' replicas are chosen, the multiple copies of a given
 chunk are laid out on consecutive drives and at consecutive offsets.
@@ -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