NetBSD/sbin/raidctl/raidctl.8

.\"     $NetBSD: raidctl.8,v 1.4 1999/02/18 07:54:33 msaitoh Exp $
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.\" by Greg Oster
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.\" Copyright (c) 1995 Carnegie-Mellon University.
.\" All rights reserved.
.\" 
.\" Author: Mark Holland
.\" 
.\" Permission to use, copy, modify and distribute this software and
.\" its documentation is hereby granted, provided that both the copyright
.\" notice and this permission notice appear in all copies of the
.\" software, derivative works or modified versions, and any portions
.\" thereof, and that both notices appear in supporting documentation.
.\" 
.\" CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
.\" CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
.\" FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
.\" 
.\" Carnegie Mellon requests users of this software to return to
.\" 
.\"  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
.\"  School of Computer Science
.\"  Carnegie Mellon University
.\"  Pittsburgh PA 15213-3890
.\" 
.\" any improvements or extensions that they make and grant Carnegie the
.\" rights to redistribute these changes.
.\" 
.Dd November 6, 1998
.Dt RAIDCTL 8
.Os NetBSD
.Sh NAME
.Nm raidctl
.Nd configuration utility for the RAIDframe disk driver
.Sh SYNOPSIS
.Nm
.Fl c Ar config_file Ar dev
.Nm ""
.Fl C Ar dev
.Nm ""
.Fl f Ar component Ar dev
.Nm ""
.Fl F Ar component Ar dev
.Nm ""
.Fl r Ar dev
.Nm ""
.Fl R Ar dev
.Nm ""
.Fl s Ar dev 
.Nm ""
.Fl u Ar dev
.Sh DESCRIPTION
.Nm
is the user-land control program for
.Xr raid 4 , Ns
the RAIDframe disk device.  
.Nm 
is primarily used to dynamically configure and unconfigure RAIDframe disk
devices.  For more information about the RAIDframe disk device, see
.Xr raid 4 .
.Pp
This document assumes the reader has at least rudimentary knowledge of
RAID and RAID concepts.
.Pp
The command-line options for 
.Nm
are as follows:
.Bl -tag -width indent
.It Fl c Ar config_file Ar dev
Configure the RAIDframe device 
.Ar dev
according to the configuration given in
.Ar config_file .
A description of the contents of 
.Ar config_file
is given later.
.It Fl C Ar dev
Initiate a copyback of reconstructed data from a spare disk to 
it's original disk.  This is performed after a component has failed, 
and the failed drive has been reconstructed onto a spare drive.
.It Fl f Ar component Ar dev
This marks the specified 
.Ar component
as having failed, but does not initiate a reconstruction of that
component.  
.It Fl F Ar component Ar dev
Fails the specified 
.Ar component
of the device, and immediately begin a reconstruction of the failed
disk onto an available hot spare.  This is the mechanism used to start
the reconstruction process if a component does have a hardware failure.
.It Fl r Ar dev
Re-write the parity on the device.  This 
.Ar MUST
be done before the RAID device is labeled and before
filesystems are created on the RAID device, and is normally used after
a system crash (and before a 
.Xr fsck 8 ) Ns
to ensure the integrity of the parity.
.It Fl R Ar dev
Check the status of component reconstruction.  The output indicates 
the amount of progress achieved in reconstructing a failed component.
.It Fl s Ar dev
Display the status of the RAIDframe device for each of the components
and spares.  
.It Fl u Ar dev
Unconfigure the RAIDframe device.
.El
.Pp
The device used by 
.Nm
is specified by 
.Ar dev .  
.Ar dev
may be either the full name of the device, e.g. /dev/rraid0d,
for the i386 architecture, and /dev/rraid0c
for all others, or just simply raid0 (for /dev/rraid0d).
.Pp
The format of the configuration file is complex, and
only an abbreviated treatment is given here.  In the configuration
files, a 
.Sq #
indicates the beginning of a comment.
.Pp
There are 4 required sections of a configuration file, and 2
optional components.  Each section begins with a 
.Sq START , 
followed by
the section name, and the confuration parameters associated with that
section.  The first section is the 
.Sq array
section, and it specifies
the number of rows, columns, and spare disks in the RAID array.  For
example: 
.Bd -unfilled -offset indent
START array
1 3 0
.Ed
.Pp
indicates an array with 1 row, 3 columns, and 0 spare disks.  Note
that although multi-dimenstional arrays may be specified, they are 
.Ar NOT
supported in the driver.
.Pp
The second section, the 
.Sq disks
section, specifies the actual
components of the device.  For example:
.Bd -unfilled -offset indent
START disks
/dev/sd0e
/dev/sd1e
/dev/sd2e
.Ed
.Pp
specifies the three component disks to be used in the RAID device.  If
any of the specified drives cannot be found when the RAID device is
configured, then they will be marked as 
.Sq failed , 
and the system will
operate in degraded mode.  Note that it is 
.Ar imperative
that the order of the components in the configuration file does not
change between configurations of a RAID device.  Changing the order
of the components (at least at the time of this writing) will result in
data loss.  
.Pp
The next section, which is the 
.Sq spare
section, is optional, and, if
present, specifies the devices to be used as 
.Sq hot spares
-- devices
which are on-line, but are not actively used by the RAID driver unless
one of the main components fail.  A simple 
.Sq spare
section might be:
.Bd -unfilled -offset indent
START spare 
/dev/sd3e
.Ed
.Pp
for a configuration with a single spare component.  If no spare drives
are to be used in the configuration, then the 
.Sq spare
section may be omitted.  
.Pp
The next section is the 
.Sq layout
section.  This section describes the
general layout parameters for the RAID device, and provides such
information as sectors per stripe unit, stripe units per parity unit,
stripe units per reconstruction unit, and the parity configuration to
use.  This section might look like:
.Bd -unfilled -offset indent
START layout
# sectPerSU SUsPerParityUnit SUsPerReconUnit RAID_level
32 1 1 5
.Ed
.Pp
The sectors per stripe unit specifies, in blocks, the interleave
factor; i.e. the number of contiguous sectors to be written to each
component for a single stripe.  Appropriate selection of this value
(32 in this example) is the subject of much research in RAID
architectures.  The stripe units per parity unit and
stripe units per reconstruction unit are normally each set to 1.
While certain values above 1 are permitted, a discussion of valid
values and the consequences of using anything other than 1 are outside
the scope of this document.  The last value in this section (5 in this
example) indicates the parity configuration desired.  Valid entries
include: 
.Bl -tag -width inde
.It 0 
RAID level 0.  No parity, only simple striping.
.It 1
RAID level 1.  Mirroring.
.It 4
RAID level 4.  Striping across components, with parity stored on the
last component.
.It 5
RAID level 5.  Striping across components, parity distributed across
all components.
.El
.Pp
There are other valid entries here, including those for Even-Odd
parity, RAID level 5 with rotated sparing, Chained declustering, 
and Interleaved declustering, but as of this writing the code for
those parity operations has not been tested with 
.Nx .
.Pp
The next required section is the 
.Sq queue
section.  This is most often
specified as:
.Bd -unfilled -offset indent
START queue
fifo 1
.Ed
.Pp
where the queueing method is specified as fifo (first-in, first-out),
and the size of the per-component queue is limited to 1 requests.  A
value of 1 is quite conservative here, and values of 100 or more may
been used to increase the driver performance. 
Other queuing methods may also be specified, but a discussion of them
is beyond the scope of this document.
.Pp
The final section, the 
.Sq debug
section, is optional.  For more details
on this the reader is referred to the RAIDframe documentation
dissussed in the 
.Sx HISTORY
section.

See
.Sx EXAMPLES
for a more complete configuration file example.

.Sh EXAMPLES

The examples in this section will focus on a RAID 5 configuration.
Other RAID configurations will behave similarly.  It is highly
recommended that before using the RAID driver for real filesystems
that the system administrator(s) have used 
.Ar all
of the options for 
.Nm ,
and that they understand how the component reconstruction process
works.  While this example is not created as a tutorial, the steps
shown here can be easily dupilicated using four equal-sized partitions
from any number of disks (including all four from a single disk).  
.Pp
The primary uses of 
.Nm
is to configure and unconfigure
.Xr raid 4 
devices.  To configure the device, a configuration
file which looks something like:
.Bd -unfilled -offset indent
START array
# numRow numCol numSpare
1 3 1

START disks
/dev/sd1e
/dev/sd2e
/dev/sd3e

START spare
/dev/sd4e

START layout
# sectPerSU SUsPerParityUnit SUsPerReconUnit RAID_level_5
32 1 1 5

START queue
fifo 100
.Ed
.Pp
is first created.  In short, this configuration file specifies a RAID
5 configuration consisting of the disks /dev/sd1e, /dev/sd2e, and
/dev/sd3e, with /dev/sd4e available as a 
.Sq hot spare
in case one of
the three main drives should fail.  If the above configuration is in a
file called 
.Sq rfconfig , 
raid device 0 can be configured with: 
.Bd -unfilled -offset indent
raidctl -c rfconfig raid0
.Ed
.Pp
The above is equivalent to the following:
.Bd -unfilled -offset indent
raidctl -c rfconfig /dev/rraid0d
.Ed
.Pp
on the i386 architecture.  On all other architectures, /dev/rraid0c
is used in place of /dev/rraid0d.
.Pp
To see how the device is doing, the following will show the status:
.Bd -unfilled -offset indent
raidctl -s raid0
.Ed
.Pp
The output will look something like:
.Bd -unfilled -offset indent
Components:
           /dev/sd1e: optimal
           /dev/sd2e: optimal
           /dev/sd3e: optimal
Spares:
           /dev/sd4e [0][0]: spare
.Ed
.Pp
This indicates that all is well with the RAID array.  If this is the first
time this RAID array has been configured, or the system is just being
brought up after an unclean shutdown, it is necessary to
ensure that the parity values are correct.  This can be done via:
.Bd -unfilled -offset indent
raidctl -r raid0
.Ed
.Pp
Once this is done, it is then safe to perform
.Xr disklabel 8 , Ns
.Xr newfs 8 , Ns
or
.Xr fsck 8
on the device or its filesystems.
.Pp
If for some reason
(perhaps to test reconstruction) it is necessary to pretend a drive
has failed, the following will perform that function:
.Bd -unfilled -offset indent
raidctl -f /dev/sd2e raid0
.Ed
.Pp
The system will then be performing all operations in degraded mode,
were missing data is re-computed from existing data and the parity.
In this case, obtaining the status of raid0 will return:
.Bd -unfilled -offset indent
Components:
           /dev/sd1e: optimal
           /dev/sd2e: failed
           /dev/sd3e: optimal
Spares:
           /dev/sd4e [0][0]: spare
.Ed
.Pp
Note that with the use of 
.Fl f
a reconstruction has not been started.  To both fail the disk and
start a reconstruction, the 
.Fl F
option must be used.  (The 
.Fl f
option may be used first, and then the
.Fl F
option used later, on the same disk, if desired.)  
Immediately after the reconstruction is started, the status will report:
.Bd -unfilled -offset indent
Components:
           /dev/sd1e: optimal
           /dev/sd2e: reconstructing
           /dev/sd3e: optimal
Spares:
           /dev/sd4e [0][0]: used_spare
.Ed
.Pp
This indicates that a reconstruction is in progress.  To find out how
the reconstruction is progressing the 
.Fl R
option may be used.  This will indicate the progress in terms of the
percentage of the reconstruction that is completed.  When the
reconstruction is finished the
.Fl s
option will show:
.Bd -unfilled -offset indent
Components:
           /dev/sd1e: optimal
           /dev/sd2e: spared
           /dev/sd3e: optimal
Spares:
           /dev/sd4e [0][0]: used_spare
.Ed
.Pp
At this point there are at least two options.  First, if /dev/sd2e is
known to be good (i.e. the failure was either caused by 
.Fl f
or 
.Fl F ,
or the failed disk was replaced), then a copyback of the data can 
be initiated with the 
.Fl C
option.  In this example, this would copy the entire contents of
/dev/sd4e to /dev/sd2e.  Once the copyback procedure is complete, the
status of the device would be:
.Bd -unfilled -offset indent
Components:
           /dev/sd1e: optimal
           /dev/sd2e: optimal
           /dev/sd3e: optimal
Spares:
           /dev/sd4e [0][0]: spare
.Ed
.Pp
and the system is back to normal operation.
.Pp
The second option after the reconstruction is to simply use /dev/sd4e
in place of /dev/sd2e in the configuration file.  For example, the
configuration file (in part) might now look like:
.Bd -unfilled -offset indent
START array
1 3 0

START drives
/dev/sd1e
/dev/sd4e
/dev/sd3e
.Ed
.Pp
This can be done as /dev/sd4e is completely interchangeable with
/dev/sd2e at this point.  Note that extreme care must be taken when 
changing the order of the drives in a configuration.  This is one of
the few instances where the devices and/or their orderings can be
changed without loss of data!  In general, the ordering of components
in a configuration file should 
.Ar never 
be changed.
.Pp
The final operation performed by 
.Nm
is to unconfigure a 
.Xr raid 4
device.  This is accomplished via a simple:
.Bd -unfilled -offset indent
raidctl -u raid0
.Ed
.Pp
at which point the device is ready to be reconfigured.
.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
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 filesystem being lost.
RAID is 
.Ar NOT
a substitute for good backup practices.
.Pp
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
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
0 there is no perception of increased data security.
.Pp
.Sh FILES
.Bl -tag -width /dev/XXrXraidX -compact
.It Pa /dev/{,r}raid*
.Nm
device special files.
.El
.Pp
.Sh SEE ALSO
.Xr raid 4 ,
.Xr ccd 4 ,
.Xr rc 8
.Sh HISTORY
RAIDframe is a framework for rapid prototyping of RAID structures
developed by the folks at the Parallel Data Laboratory at Carnegie
Mellon University (CMU).  
A more complete description of the internals and functionality of
RAIDframe is found in the paper "RAIDframe: A Rapid Prototyping Tool
for RAID Systems", by William V. Courtright II, Garth Gibson, Mark
Holland, LeAnn Neal Reilly, and Jim Zelenka, and published by the
Parallel Data Laboratory of Carnegie Mellon University.
.Pp
The
.Nm
command first appeared as a program in CMU's RAIDframe v1.1 distribution.  This
version of
.Nm
is a complete re-write, and first appeared in
.Nx 1.4 .
.Sh COPYRIGHT
.Bd -unfilled

The RAIDframe Copyright is as follows:

Copyright (c) 1994-1996 Carnegie-Mellon University.
All rights reserved.

Permission to use, copy, modify and distribute this software and
its documentation is hereby granted, provided that both the copyright
notice and this permission notice appear in all copies of the
software, derivative works or modified versions, and any portions
thereof, and that both notices appear in supporting documentation.

CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.

Carnegie Mellon requests users of this software to return to

 Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 School of Computer Science
 Carnegie Mellon University
 Pittsburgh PA 15213-3890

any improvements or extensions that they make and grant Carnegie the
rights to redistribute these changes.

.Ed