Module Name: src
Committed By: wiz
Date: Mon May 4 20:37:07 UTC 2009
Modified Files:
src/share/man/man4: raid.4
Log Message:
New sentence, new line. Sort SEE ALSO.
To generate a diff of this commit:
cvs rdiff -u -r1.35 -r1.36 src/share/man/man4/raid.4
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/share/man/man4/raid.4
diff -u src/share/man/man4/raid.4:1.35 src/share/man/man4/raid.4:1.36
--- src/share/man/man4/raid.4:1.35 Fri May 2 18:11:05 2008
+++ src/share/man/man4/raid.4 Mon May 4 20:37:07 2009
@@ -1,4 +1,4 @@
-.\" $NetBSD: raid.4,v 1.35 2008/05/02 18:11:05 martin Exp $
+.\" $NetBSD: raid.4,v 1.36 2009/05/04 20:37:07 wiz Exp $
.\"
.\" Copyright (c) 1998 The NetBSD Foundation, Inc.
.\" All rights reserved.
@@ -87,7 +87,8 @@
.Nx .
This
document assumes that the reader has at least some familiarity with RAID
-and RAID concepts. The reader is also assumed to know how to configure
+and RAID concepts.
+The reader is also assumed to know how to configure
disks and pseudo-devices into kernels, how to generate kernels, and how
to partition disks.
.Pp
@@ -110,12 +111,16 @@
at the end of this section.
.Pp
Depending on the parity level configured, the device driver can
-support the failure of component drives. The number of failures
-allowed depends on the parity level selected. If the driver is able
+support the failure of component drives.
+The number of failures
+allowed depends on the parity level selected.
+If the driver is able
to handle drive failures, and a drive does fail, then the system is
-operating in "degraded mode". In this mode, all missing data must be
+operating in "degraded mode".
+In this mode, all missing data must be
reconstructed from the data and parity present on the other
-components. This results in much slower data accesses, but
+components.
+This results in much slower data accesses, but
does mean that a failure need not bring the system to a complete halt.
.Pp
The RAID driver supports and enforces the use of
@@ -139,7 +144,8 @@
or that the component label is not consistent with its assigned place
in the set (e.g. the component label claims the component should be
the 3rd one in a 6-disk set, but the RAID set has it as the 3rd component
-in a 5-disk set) then the device will fail to configure. If the
+in a 5-disk set) then the device will fail to configure.
+If the
driver determines that exactly one component label seems to be
incorrect, and the RAID set is being configured as a set that supports
a single failure, then the RAID set will be allowed to configure, but
@@ -150,17 +156,21 @@
will configure normally.
.Pp
Component labels are also used to support the auto-detection and
-autoconfiguration of RAID sets. A RAID set can be flagged as
+autoconfiguration of RAID sets.
+A RAID set can be flagged as
autoconfigurable, in which case it will be configured automatically
-during the kernel boot process. RAID file systems which are
+during the kernel boot process.
+RAID file systems which are
automatically configured are also eligible to be the root file system.
There is currently only limited support (alpha, amd64, i386, pmax,
sparc, sparc64, and vax architectures)
for booting a kernel directly from a RAID 1 set, and no support for
-booting from any other RAID sets. To use a RAID set as the root
+booting from any other RAID sets.
+To use a RAID set as the root
file system, a kernel is usually obtained from a small non-RAID
partition, after which any autoconfiguring RAID set can be used for the
-root file system. See
+root file system.
+See
.Xr raidctl 8
for more information on autoconfiguration of RAID sets.
Note that with autoconfiguration of RAID sets, it is no longer
@@ -172,14 +182,17 @@
The driver supports
.Sq hot spares ,
disks which are on-line, but are not
-actively used in an existing file system. Should a disk fail, the
+actively used in an existing file system.
+Should a disk fail, the
driver is capable of reconstructing the failed disk onto a hot spare
or back onto a replacement drive.
If the components are hot swappable, the failed disk can then be
removed, a new disk put in its place, and a copyback operation
-performed. The copyback operation, as its name indicates, will copy
+performed.
+The copyback operation, as its name indicates, will copy
the reconstructed data from the hot spare to the previously failed
-(and now replaced) disk. Hot spares can also be hot-added using
+(and now replaced) disk.
+Hot spares can also be hot-added using
.Xr raidctl 8 .
.Pp
If a component cannot be detected when the RAID device is configured,
@@ -194,11 +207,14 @@
.Xr raidctl 8
must be used with the
.Fl i
-option to initialize all RAID sets. In particular, this
-initialization includes re-building the parity data. This rebuilding
+option to initialize all RAID sets.
+In particular, this
+initialization includes re-building the parity data.
+This rebuilding
of parity data is also required when either a) a new RAID device is
brought up for the first time or b) after an un-clean shutdown of a
-RAID device. By using the
+RAID device.
+By using the
.Fl P
option to
.Xr raidctl 8 ,
@@ -207,28 +223,31 @@
.Xr fsck 8
or a
.Xr newfs 8 ,
-file system integrity and parity integrity can be ensured. It bears
-repeating again that parity recomputation is
+file system integrity and parity integrity can be ensured.
+It bears repeating again that parity recomputation is
.Ar required
-before any file systems are created or used on the RAID device. If the
+before any file systems are created or used on the RAID device.
+If the
parity is not correct, then missing data cannot be correctly recovered.
.Pp
-RAID levels may be combined in a hierarchical fashion. For example, a RAID 0
+RAID levels may be combined in a hierarchical fashion.
+For example, a RAID 0
device can be constructed out of a number of RAID 5 devices (which, in turn,
may be constructed out of the physical disks, or of other RAID devices).
.Pp
The first step to using the
.Nm
-driver is to ensure that it is suitably configured in the kernel. This is
-done by adding a line similar to:
+driver is to ensure that it is suitably configured in the kernel.
+This is done by adding a line similar to:
.Bd -unfilled -offset indent
pseudo-device raid 4 # RAIDframe disk device
.Ed
.Pp
-to the kernel configuration file. The
+to the kernel configuration file.
+The
.Sq count
-argument (
-.Sq 4 ,
+argument
+.Sq ( 4 ,
in this case), specifies the number of RAIDframe drivers to configure.
To turn on component auto-detection and autoconfiguration of RAID
sets, simply add:
@@ -243,7 +262,8 @@
(e.g. 4.2BSD) or
.Dv FS_RAID .
The use of the latter is strongly encouraged, and is required if
-autoconfiguration of the RAID set is desired. Since RAIDframe leaves
+autoconfiguration of the RAID set is desired.
+Since RAIDframe leaves
room for disklabels, RAID components can be simply raw disks, or
partitions which use an entire disk.
.Pp
@@ -254,7 +274,8 @@
It is highly recommended that the steps to reconstruct, copyback, and
re-compute parity are well understood by the system administrator(s)
.Ar before
-a component failure. Doing the wrong thing when a component fails may
+a component failure.
+Doing the wrong thing when a component fails may
result in data loss.
.Pp
Additional internal consistency checking can be enabled by specifying:
@@ -372,7 +393,8 @@
section for more detail on these various RAID configurations.
.Sh WARNINGS
Certain RAID levels (1, 4, 5, 6, and others) can protect against some
-data loss due to component failure. However the loss of two
+data loss due to component failure.
+However the loss of two
components of a RAID 4 or 5 system, or the loss of a single component
of a RAID 0 system, will result in the entire file systems on that RAID
device being lost.
@@ -383,11 +405,14 @@
Recomputation of parity
.Ar MUST
be performed whenever there is a chance that it may have been
-compromised. This includes after system crashes, or before a RAID
-device has been used for the first time. Failure to keep parity
+compromised.
+This includes after system crashes, or before a RAID
+device has been used for the first time.
+Failure to keep parity
correct will be catastrophic should a component ever fail -- it is
better to use RAID 0 and get the additional space and speed, than it
-is to use parity, but not keep the parity correct. At least with RAID
+is to use parity, but not keep the parity correct.
+At least with RAID
0 there is no perception of increased data security.
.Sh FILES
.Bl -tag -width /dev/XXrXraidX -compact
@@ -398,8 +423,8 @@
.Sh SEE ALSO
.Xr config 1 ,
.Xr sd 4 ,
-.Xr MAKEDEV 8 ,
.Xr fsck 8 ,
+.Xr MAKEDEV 8 ,
.Xr mount 8 ,
.Xr newfs 8 ,
.Xr raidctl 8
@@ -410,10 +435,12 @@
.Nx
is a port of RAIDframe, a framework for rapid prototyping of RAID
structures developed by the folks at the Parallel Data Laboratory at
-Carnegie Mellon University (CMU). RAIDframe, as originally distributed
+Carnegie Mellon University (CMU).
+RAIDframe, as originally distributed
by CMU, provides a RAID simulator for a number of different
architectures, and a user-level device driver and a kernel device
-driver for Digital Unix. The
+driver for Digital Unix.
+The
.Nm
driver is a kernelized version of RAIDframe v1.1.
.Pp
