OpenBSD-4.6/sbin/raidctl/raidctl.8
.\" $OpenBSD: raidctl.8,v 1.41 2008/06/26 05:42:06 ray Exp $
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.Dd $Mdocdate: June 26 2008 $
.Dt RAIDCTL 8
.Os
.Sh NAME
.Nm raidctl
.Nd configuration utility for the RAIDframe disk driver
.Sh SYNOPSIS
.Nm raidctl
.Bk -words
.Op Fl BGiPpSsuv
.Op Fl A Op yes | no | root
.Op Fl Cc Ar config_file
.Op Fl I Ar serial_number
.Op Fl aFfgRr Ar component
.Ar dev
.Ek
.Sh DESCRIPTION
.Nm
is the user-land control program for
.Xr raid 4 ,
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 device used by
.Nm
is specified by
.Ar dev .
.Ar dev
may be either the full name of the device, e.g.\&
.Pa /dev/rraid0c ,
or just simply raid0 (for
.Pa /dev/rraid0c ) .
.Pp
For several commands
.Pq Fl BGipPsSu ,
.Nm
can accept the word
.Ic all
as the
.Ar dev
argument.
If
.Ic all
is used,
.Nm
will execute the requested action for all the configured
.Xr raid 4
devices.
.Pp
The command-line options for
.Nm
are as follows:
.Bl -tag -width indent
.It Fl A Ic yes Ar dev
Make the RAID set auto-configurable.
The RAID set will be automatically configured at boot
.Em before
the root file system is
mounted.
Note that all components of the set must be of type RAID in the disklabel.
.It Fl A Ic no Ar dev
Turn off auto-configuration for the RAID set.
.It Fl A Ic root Ar dev
Make the RAID set auto-configurable, and also mark the set as being
eligible to contain the root partition.
A RAID set configured this way will
.Em override
the use of the boot disk as the root device.
All components of the set must be of type RAID in the disklabel.
Note that the kernel being booted must currently reside on a non-RAID set and,
in order to have the root file system correctly mounted from it,
the RAID set must have its
.Sq a
partition (aka raid[0..n]a) set up.
.It Fl a Ar component Ar dev
Add
.Ar component
as a hot spare for the device
.Ar dev .
.It Fl B Ar dev
Initiate a copyback of reconstructed data from a spare disk to
its original disk.
This is performed after a component has failed,
and the failed drive has been reconstructed onto a spare drive.
.It Fl C Ar config_file Ar dev
As for
.Fl c ,
but forces the configuration to take place.
This is required the first time a RAID set is configured.
.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 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 one of the mechanisms used to start the reconstruction process
if a component does have a hardware failure.
.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 G Ar dev
Generate the configuration of the RAIDframe device in a format suitable for
use with
.Nm
.Fl c
or
.Fl C .
.It Fl g Ar component Ar dev
Get the component label for the specified component.
.It Fl I Ar serial_number Ar dev
Initialize the component labels on each component of the device.
.Ar serial_number
is used as one of the keys in determining whether a
particular set of components belong to the same RAID set.
While not strictly enforced, different serial numbers should be used for
different RAID sets.
This step
.Em MUST
be performed when a new RAID set is created.
.It Fl i Ar dev
Initialize the RAID device.
In particular, (re-write) the parity on the selected device.
This
.Em MUST
be done for
.Em all
RAID sets before the RAID device is labeled and before
file systems are created on the RAID device.
.It Fl P Ar dev
Check the status of the parity on the RAID set, and initialize
(re-write) the parity if the parity is not known to be up-to-date.
This is normally used after a system crash (and before a
.Xr fsck 8 )
to ensure the integrity of the parity.
.It Fl p Ar dev
Check the status of the parity on the RAID set.
Displays a status message, and returns successfully if the parity
is up-to-date.
.It Fl R Ar component Ar dev
Fails the specified
.Ar component ,
if necessary, and immediately begins a reconstruction back to
.Ar component .
This is useful for reconstructing back onto a component after
it has been replaced following a failure.
.It Fl r Ar component Ar dev
Remove the spare disk specified by
.Ar component
from the set of available spare components.
.It Fl S Ar dev
Check the status of parity re-writing, component reconstruction, and
component copyback.
The output indicates the amount of progress achieved in each of these areas.
.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.
.It Fl v
Be more verbose.
For operations such as reconstructions, parity re-writing,
and copybacks, provide a progress indicator.
.El
.Ss Configuration file
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 sections.
Each section begins with a
.Sq START ,
followed by
the section name, and the configuration 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 set.
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-dimensional arrays may be specified, they are
.Em 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
.Em 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 will result in data loss if the set
is configured with the
.Fl C
option.
In normal circumstances, the RAID set will not configure if only
.Fl c
is specified, and the components are out-of-order.
.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.
The parity is the mirror.
.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
.Ox .
.Pp
The next required section is the
.Sq queue
section.
This is most often specified as:
.Bd -unfilled -offset indent
START queue
fifo 100
.Ed
.Pp
where the queuing method is specified as FIFO (First-In, First-Out),
and the size of the per-component queue is limited to 100 requests.
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 discussed in the
.Sx HISTORY
section.
See
.Sx EXAMPLES
for a more complete configuration file example.
.Sh EXAMPLES
It is highly recommended that before using the RAID driver for real
file systems that the system administrator(s) become quite familiar
with the use of
.Nm raidctl ,
and that they understand how the component reconstruction process
works.
The examples in this section will focus on configuring a
number of different RAID sets of varying degrees of redundancy.
By working through these examples, administrators should be able to
develop a good feel for how to configure a RAID set, and how to
initiate reconstruction of failed components.
.Pp
In the following examples
.Sq raid0
will be used to denote the RAID device.
.Sq Pa /dev/rraid0c
may be used in place of
.Sq raid0 .
.Ss Initialization and Configuration
The initial step in configuring a RAID set is to identify the components
that will be used in the RAID set.
All components should be the same size.
Each component should have a disklabel type of
.Dv FS_RAID ,
and a typical disklabel entry for a RAID component might look like:
.Bd -unfilled -offset indent
f: 1800000 200495 RAID # (Cyl. 405*- 4041*)
.Ed
.Pp
While
.Dv FS_BSDFFS
(e.g. 4.2BSD) will also work as the component type, the type
.Dv FS_RAID
(e.g. RAID) is preferred for RAIDframe use, as it is required for
features such as auto-configuration.
As part of the initial configuration of each RAID set, each component
will be given a
.Sq component label .
A
.Sq component label
contains important information about the component, including a
user-specified serial number, the row and column of that component in
the RAID set, the redundancy level of the RAID set, a 'modification
counter', and whether the parity information (if any) on that
component is known to be correct.
Component labels are an integral part of the RAID set, since they are used
to ensure that components are configured in the correct order, and used
to keep track of other vital information about the RAID set.
Component labels are also required for the auto-detection and
auto-configuration of RAID sets at boot time.
For a component label to be considered valid, that particular component label
must be in agreement with the other component labels in the set.
For example, the serial number,
.Sq modification counter ,
number of rows and number of columns must all
be in agreement.
If any of these are different, then the component is not considered to be
part of the set.
See
.Xr raid 4
for more information about component labels.
.Pp
Once the components have been identified, and the disks have
appropriate labels,
.Nm
is then used to configure the
.Xr raid 4
device.
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 created in a file.
The above configuration file specifies a RAID 5 set consisting of
the components
.Pa /dev/sd1e , /dev/sd2e ,
and
.Pa /dev/sd3e ,
with
.Pa /dev/sd4e
available as a
.Sq hot spare
in case one of
the three main drives should fail.
A RAID 0 set would be specified in a similar way:
.Bd -unfilled -offset indent
START array
# numRow numCol numSpare
1 4 0
START disks
/dev/sd10e
/dev/sd11e
/dev/sd12e
/dev/sd13e
START layout
# sectPerSU SUsPerParityUnit SUsPerReconUnit RAID_level_0
64 1 1 0
START queue
fifo 100
.Ed
.Pp
In this case, devices
.Pa /dev/sd10e , /dev/sd11e , /dev/sd12e ,
and
.Pa /dev/sd13e
are the components that make up this RAID set.
Note that there are no hot spares for a RAID 0 set, since there is no way
to recover data if any of the components fail.
.Pp
For a RAID 1 (mirror) set, the following configuration might be used:
.Bd -unfilled -offset indent
START array
# numRow numCol numSpare
1 2 0
START disks
/dev/sd20e
/dev/sd21e
START layout
# sectPerSU SUsPerParityUnit SUsPerReconUnit RAID_level_1
128 1 1 1
START queue
fifo 100
.Ed
.Pp
In this case,
.Pa /dev/sd20e
and
.Pa /dev/sd21e
are the two components of the
mirror set.
While no hot spares have been specified in this configuration,
they easily could be, just as they were specified in the RAID 5 case above.
Note as well that RAID 1 sets are currently limited to only 2 components.
At present, n-way mirroring is not possible.
.Pp
The first time a RAID set is configured, the
.Fl C
option must be used:
.Bd -unfilled -offset indent
# raidctl -C raid0.conf raid0
.Ed
.Pp
where
.Sq raid0.conf
is the name of the RAID configuration file.
The
.Fl C
forces the configuration to succeed, even if any of the component
labels are incorrect.
The
.Fl C
option should not be used lightly in
situations other than initial configurations, as if
the system is refusing to configure a RAID set, there is probably a
very good reason for it.
After the initial configuration is done (and appropriate component labels
are added with the
.Fl I
option) then raid0 can be configured normally with:
.Bd -unfilled -offset indent
# raidctl -c raid0.conf raid0
.Ed
.Pp
When the RAID set is configured for the first time, it is
necessary to initialize the component labels, and to initialize the
parity on the RAID set.
Initializing the component labels is done with:
.Bd -unfilled -offset indent
# raidctl -I 112341 raid0
.Ed
.Pp
where
.Sq 112341
is a user-specified serial number for the RAID set.
This initialization step is
.Em required
for all RAID sets.
Also, using different serial numbers between RAID sets is
.Em strongly encouraged ,
as using the same serial number for all RAID sets will only serve to
decrease the usefulness of the component label checking.
.Pp
Initializing the RAID set is done via the
.Fl i
option.
This initialization
.Em MUST
be done for
.Em all
RAID sets, since among other things it verifies that the parity (if
any) on the RAID set is correct.
Since this initialization may be quite time-consuming, the
.Fl v
option may be also used in conjunction with
.Fl i :
.Bd -unfilled -offset indent
# raidctl -iv raid0
.Ed
.Pp
This will give more verbose output on the
status of the initialization:
.Bd -unfilled -offset indent
Initiating re-write of parity
Parity Re-write status:
10% |**** | ETA: 06:03 /
.Ed
.Pp
The output provides a
.Sq Percent Complete
in both a numeric and graphical format, as well as an estimated time
to completion of the operation.
.Pp
Since it is the parity that provides the
.Sq redundancy
part of RAID, it is critical that the parity is correct
as much as possible.
If the parity is not correct, then there is no guarantee that data will not
be lost if a component fails.
.Pp
Once the parity is known to be correct, it is then safe to perform
.Xr disklabel 8 ,
.Xr newfs 8 ,
or
.Xr fsck 8
on the device or its filesystems, and then to mount the filesystems
for use.
.Pp
Under certain circumstances (e.g. the additional component has not
arrived, or data is being migrated off of a disk destined to become a
component) it may be desirable to configure a RAID 1 set with only
a single component.
This can be achieved by configuring the set with a physically existing
component (as either the first or second component) and with a
.Sq fake
component.
In the following:
.Bd -unfilled -offset indent
START array
# numRow numCol numSpare
1 2 0
START disks
/dev/sd6e
/dev/sd0e
START layout
# sectPerSU SUsPerParityUnit SUsPerReconUnit RAID_level_1
128 1 1 1
START queue
fifo 100
.Ed
.Pp
.Pa /dev/sd0e
is the real component, and will be the second disk of a RAID 1
set.
The component
.Pa /dev/sd6e ,
which must exist, but have no physical
device associated with it, is simply used as a placeholder.
Configuration (using
.Fl C
and
.Fl I Ar 12345
as above) proceeds normally, but initialization of the RAID set will
have to wait until all physical components are present.
After configuration, this set can be used normally, but will be operating
in degraded mode.
Once a second physical component is obtained, it can be hot-added,
the existing data mirrored, and normal operation resumed.
.Ss Maintenance of the RAID set
After the parity has been initialized for the first time, the command:
.Bd -unfilled -offset indent
# raidctl -p raid0
.Ed
.Pp
can be used to check the current status of the parity.
To check the parity and rebuild it necessary (for example, after an unclean
shutdown) the command:
.Bd -unfilled -offset indent
# raidctl -P raid0
.Ed
.Pp
is used.
Note that re-writing the parity can be done while other operations on the
RAID set are taking place (e.g. while doing an
.Xr fsck 8
on a file system on the RAID set).
However: for maximum effectiveness of the RAID set, the parity should be
known to be correct before any data on the set is modified.
.Pp
To see how the RAID set is doing, the following command can be used to
show the RAID set's 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: spare
Parity status: clean
Reconstruction is 100% complete.
Parity Re-write is 100% complete.
Copyback is 100% complete.
.Ed
.Pp
This indicates that all is well with the RAID set.
Of importance here are the component lines which read
.Sq optimal ,
and the
.Sq Parity status
line which indicates that the parity is up-to-date.
Note that if there are file systems open on the RAID set,
the individual components will not be
.Sq clean
but the set as a whole can still be clean.
.Pp
The
.Fl v
option may be also used in conjunction with
.Fl s :
.Bd -unfilled -offset indent
# raidctl -sv raid0
.Ed
.Pp
In this case, the components' label information (see the
.Fl g
option) will be given as well:
.Bd -unfilled -offset indent
Components:
/dev/sd1e: optimal
/dev/sd2e: optimal
/dev/sd3e: optimal
Spares:
/dev/sd4e: spare
Component label for /dev/sd1e:
Row: 0 Column: 0 Num Rows: 1 Num Columns: 3
Version: 2 Serial Number: 13432 Mod Counter: 65
Clean: No Status: 0
sectPerSU: 32 SUsPerPU: 1 SUsPerRU: 1
RAID Level: 5 blocksize: 512 numBlocks: 1799936
Autoconfig: No
Last configured as: raid0
Component label for /dev/sd2e:
Row: 0 Column: 1 Num Rows: 1 Num Columns: 3
Version: 2 Serial Number: 13432 Mod Counter: 65
Clean: No Status: 0
sectPerSU: 32 SUsPerPU: 1 SUsPerRU: 1
RAID Level: 5 blocksize: 512 numBlocks: 1799936
Autoconfig: No
Last configured as: raid0
Component label for /dev/sd3e:
Row: 0 Column: 2 Num Rows: 1 Num Columns: 3
Version: 2 Serial Number: 13432 Mod Counter: 65
Clean: No Status: 0
sectPerSU: 32 SUsPerPU: 1 SUsPerRU: 1
RAID Level: 5 blocksize: 512 numBlocks: 1799936
Autoconfig: No
Last configured as: raid0
Parity status: clean
Reconstruction is 100% complete.
Parity Re-write is 100% complete.
Copyback is 100% complete.
.Ed
.Pp
To check the component label of /dev/sd1e, the following is used:
.Bd -unfilled -offset indent
# raidctl -g /dev/sd1e raid0
.Ed
.Pp
The output of this command will look something like:
.Bd -unfilled -offset indent
Component label for /dev/sd1e:
Row: 0 Column: 0 Num Rows: 1 Num Columns: 3
Version: 2 Serial Number: 13432 Mod Counter: 65
Clean: No Status: 0
sectPerSU: 32 SUsPerPU: 1 SUsPerRU: 1
RAID Level: 5 blocksize: 512 numBlocks: 1799936
Autoconfig: No
Last configured as: raid0
.Ed
.Ss Dealing with Component Failures
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,
where missing data is re-computed from existing data and the parity.
In this case, obtaining the status of raid0 will return (in part):
.Bd -unfilled -offset indent
Components:
/dev/sd1e: optimal
/dev/sd2e: failed
/dev/sd3e: optimal
Spares:
/dev/sd4e: 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:
.Bd -unfilled -offset indent
# raidctl -F /dev/sd2e raid0
.Ed
.Pp
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: used_spare
[...]
Parity status: clean
Reconstruction is 10% complete.
Parity Re-write is 100% complete.
Copyback is 100% complete.
.Ed
.Pp
This indicates that a reconstruction is in progress.
To find out how the reconstruction is progressing the
.Fl S
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: used_spare
[...]
Parity status: clean
Reconstruction is 100% complete.
Parity Re-write is 100% complete.
Copyback is 100% complete.
.Ed
.Pp
At this point there are at least two options.
First, if
.Pa /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 B
option.
In this example, this would copy the entire contents of
.Pa /dev/sd4e
to
.Pa /dev/sd2e .
Once the copyback procedure is complete, the
status of the device would be (in part):
.Bd -unfilled -offset indent
Components:
/dev/sd1e: optimal
/dev/sd2e: optimal
/dev/sd3e: optimal
Spares:
/dev/sd4e: spare
.Ed
.Pp
and the system is back to normal operation.
.Pp
The second option after the reconstruction is to simply use
.Pa /dev/sd4e
in place of
.Pa /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
.Pa /dev/sd4e
is completely interchangeable with
.Pa /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
.Em never
be changed.
.Pp
If a component fails and there are no hot spares
available on-line, the status of the RAID set might (in part) look like:
.Bd -unfilled -offset indent
Components:
/dev/sd1e: optimal
/dev/sd2e: failed
/dev/sd3e: optimal
No spares.
.Ed
.Pp
In this case there are a number of options.
The first option is to add a hot spare using:
.Bd -unfilled -offset indent
# raidctl -a /dev/sd4e raid0
.Ed
.Pp
After the hot add, the status would then be:
.Bd -unfilled -offset indent
Components:
/dev/sd1e: optimal
/dev/sd2e: failed
/dev/sd3e: optimal
Spares:
/dev/sd4e: spare
.Ed
.Pp
Reconstruction could then take place using
.Fl F
as describe above.
.Pp
A second option is to rebuild directly onto
.Pa /dev/sd2e .
Once the disk containing
.Pa /dev/sd2e
has been replaced, one can simply use:
.Bd -unfilled -offset indent
# raidctl -R /dev/sd2e raid0
.Ed
.Pp
to rebuild the
.Pa /dev/sd2e
component.
As the rebuilding is in progress, the status will be:
.Bd -unfilled -offset indent
Components:
/dev/sd1e: optimal
/dev/sd2e: reconstructing
/dev/sd3e: optimal
No spares.
.Ed
.Pp
and when completed, will be:
.Bd -unfilled -offset indent
Components:
/dev/sd1e: optimal
/dev/sd2e: optimal
/dev/sd3e: optimal
No spares.
.Ed
.Pp
In circumstances where a particular component is completely
unavailable after a reboot, a special component name will be used to
indicate the missing component.
For example:
.Bd -unfilled -offset indent
Components:
/dev/sd2e: optimal
component1: failed
No spares.
.Ed
.Pp
indicates that the second component of this RAID set was not detected
at all by the auto-configuration code.
The name
.Sq component1
can be used anywhere a normal component name would be used.
For example, to add a hot spare to the above set, and rebuild to that hot
spare, the following could be done:
.Bd -unfilled -offset indent
# raidctl -a /dev/sd3e raid0
# raidctl -F component1 raid0
.Ed
.Pp
at which point the data missing from
.Sq component1
would be reconstructed onto
.Pa /dev/sd3e .
.Ss RAID on RAID
RAID sets can be layered to create more complex and much larger RAID
sets.
A RAID 0 set, for example, could be constructed from four RAID 5 sets.
The following configuration file shows such a setup:
.Bd -unfilled -offset indent
START array
# numRow numCol numSpare
1 4 0
START disks
/dev/raid1e
/dev/raid2e
/dev/raid3e
/dev/raid4e
START layout
# sectPerSU SUsPerParityUnit SUsPerReconUnit RAID_level_0
128 1 1 0
START queue
fifo 100
.Ed
.Pp
A similar configuration file might be used for a RAID 0 set
constructed from components on RAID 1 sets.
In such a configuration, the mirroring provides a high degree of redundancy,
while the striping provides additional speed benefits.
.Ss Auto-configuration and Root on RAID
RAID sets can also be auto-configured at boot.
To make a set auto-configurable, simply prepare the RAID set as above,
and then do a:
.Pp
.Dl # raidctl -A yes raid0
.Pp
to turn on auto-configuration for that set.
To turn off auto-configuration, use:
.Pp
.Dl # raidctl -A no raid0
.Pp
RAID sets which are auto-configurable will be configured before the
root file system is mounted.
These RAID sets are thus available for use as a root file system,
or for any other file system.
A primary advantage of using the auto-configuration is that RAID components
become more independent of the disks they reside on.
For example, SCSI ID's can change, but auto-configured sets will always be
configured correctly, even if the SCSI ID's of the component disks
have become scrambled.
.Pp
Having a system's root file system
.Pq Pa /
on a RAID set is also allowed,
with the
.Sq a
partition of such a RAID set being used for
.Pa / .
To use raid0a as the root file system, simply use:
.Bd -unfilled -offset indent
# raidctl -A root raid0
.Ed
.Pp
To return raid0 to be just an auto-configuring set simply use the
.Fl A Ar yes
arguments.
.Pp
.\" Note that kernels can only be directly read from RAID 1 components on
.\" alpha and pmax architectures.
.\" On those architectures, the
.\" .Dv FS_RAID
.\" file system is recognized by the bootblocks, and will properly load the
.\" kernel directly from a RAID 1 component.
.\" For other architectures, or
Note that kernels can't be directly read from a RAID component.
To support the root file system on RAID sets, some mechanism must be
used to get a kernel booting.
For example, a small partition containing only the secondary boot-blocks
and an alternate kernel (or two) could be used.
Once a kernel is booting however, and an auto-configured RAID
set is found that is eligible to be root, then that RAID set will be
auto-configured and its
.Sq a
partition (aka raid[0..n]a) will be used as the root file system.
If two or more RAID sets claim to be root devices, then the user will be
prompted to select the root device.
At this time, RAID 0, 1, 4, and 5 sets are all supported as root devices.
.Pp
A typical RAID 1 setup with root on RAID might be as follows:
.Bl -enum
.It
wd0a - a small partition, which contains a complete, bootable, basic
.Ox
installation.
.It
wd1a - also contains a complete, bootable, basic
.Ox
installation.
.It
wd0e and wd1e - a RAID 1 set, raid0, used for the root file system.
.It
wd0f and wd1f - a RAID 1 set, raid1, which will be used only for
swap space.
.It
wd0g and wd1g - a RAID 1 set, raid2, used for
.Pa /usr ,
.Pa /home ,
or other data, if desired.
.It
wd0h and wd1h - a RAID 1 set, raid3, if desired.
.El
.Pp
RAID sets raid0, raid1, and raid2 are all marked as
auto-configurable.
raid0 is marked as being a root-able raid.
When new kernels are installed, the kernel is not only copied to
.Pa / ,
but also to wd0a and wd1a.
The kernel on wd0a is required, since that is the kernel the system
boots from.
The kernel on wd1a is also required, since that will be the kernel used
should wd0 fail.
The important point here is to have redundant copies of the kernel
available, in the event that one of the drives fail.
.Pp
There is no requirement that the root file system be on the same disk
as the kernel.
For example, obtaining the kernel from wd0a, and using
sd0e and sd1e for raid0, and the root file system, is fine.
It
.Em is
critical, however, that there be multiple kernels available, in the
event of media failure.
.Pp
Multi-layered RAID devices (such as a RAID 0 set made
up of RAID 1 sets) are
.Em not
supported as root devices or auto-configurable devices at this point.
(Multi-layered RAID devices
.Em are
supported in general, however, as mentioned earlier.)
Note that in
order to enable component auto-detection and auto-configuration of
RAID devices, the line:
.Bd -unfilled -offset indent
option RAID_AUTOCONFIG
.Ed
.Pp
must be in the kernel configuration file.
See
.Xr raid 4
for more details.
.Ss Unconfiguration
The final operation performed by
.Nm
is to unconfigure a
.Xr raid 4
device.
This is accomplished via a simple:
.Pp
.Dl # raidctl -u raid0
.Pp
at which point the device is ready to be reconfigured.
.Ss Performance Tuning
Selection of the various parameter values which result in the best
performance can be quite tricky, and often requires a bit of
trial-and-error to get those values most appropriate for a given system.
A whole range of factors come into play, including:
.Bl -enum
.It
Types of components (e.g. SCSI vs. IDE) and their bandwidth
.It
Types of controller cards and their bandwidth
.It
Distribution of components among controllers
.It
I/O bandwidth
.It
File system access patterns
.It
CPU speed
.El
.Pp
As with most performance tuning, benchmarking under real-life loads
may be the only way to measure expected performance.
Understanding some of the underlying technology is also useful in tuning.
The goal of this section is to provide pointers to those parameters which may
make significant differences in performance.
.Pp
For a RAID 1 set, a SectPerSU value of 64 or 128 is typically sufficient.
Since data in a RAID 1 set is arranged in a linear
fashion on each component, selecting an appropriate stripe size is
somewhat less critical than it is for a RAID 5 set.
However: a stripe size that is too small will cause large I/Os to be
broken up into a number of smaller ones, hurting performance.
At the same time, a large stripe size may cause problems with concurrent
accesses to stripes, which may also affect performance.
Thus values in the range of 32 to 128 are often the most effective.
.Pp
Tuning RAID 5 sets is trickier.
In the best case, I/O is presented to the RAID set one stripe at a time.
Since the entire stripe is available at the beginning of the I/O,
the parity of that stripe can be calculated before the stripe is written,
and then the stripe data and parity can be written in parallel.
When the amount of data being written is less than a full stripe worth, the
.Sq small write
problem occurs.
Since a
.Sq small write
means only a portion of the stripe on the components is going to
change, the data (and parity) on the components must be updated
slightly differently.
First, the
.Sq old parity
and
.Sq old data
must be read from the components.
Then the new parity is constructed, using the new data to be written,
and the old data and old parity.
Finally, the new data and new parity are written.
All this extra data shuffling results in a serious loss of performance,
and is typically 2 to 4 times slower than a full stripe write (or read).
To combat this problem in the real world, it may be useful to ensure that
stripe sizes are small enough that a
.Sq large I/O
from the system will use exactly one large stripe write.
As is seen later, there are some file system dependencies which may come
into play here as well.
.Pp
Since the size of a
.Sq large I/O
is often (currently) only 32K or 64K, on a 5-drive RAID 5 set it may
be desirable to select a SectPerSU value of 16 blocks (8K) or 32
blocks (16K).
Since there are 4 data sectors per stripe, the maximum
data per stripe is 64 blocks (32K) or 128 blocks (64K).
Again, empirical measurement will provide the best indicators of which
values will yield better performance.
.Pp
The parameters used for the file system are also critical to good
performance.
For
.Xr newfs 8 ,
for example, increasing the block size to 32K or 64K may improve
performance dramatically.
Also, changing the cylinders-per-group parameter from 16 to 32 or higher
is often not only necessary for larger file systems, but may also have
positive performance implications.
.Ss Summary
Despite the length of this man-page, configuring a RAID set is a
relatively straight-forward process.
All that needs to be done is the following steps:
.Bl -enum
.It
Use
.Xr disklabel 8
to create the components (of type RAID).
.It
Construct a RAID configuration file: e.g.\&
.Sq raid0.conf
.It
Configure the RAID set with:
.Bd -unfilled -offset indent
# raidctl -C raid0.conf raid0
.Ed
.Pp
.It
Initialize the component labels with:
.Bd -unfilled -offset indent
# raidctl -I 123456 raid0
.Ed
.Pp
.It
Initialize other important parts of the set with:
.Bd -unfilled -offset indent
# raidctl -i raid0
.Ed
.Pp
.It
Get the default label for the RAID set:
.Bd -unfilled -offset indent
# disklabel raid0 > /tmp/label
.Ed
.Pp
.It
Edit the label:
.Bd -unfilled -offset indent
# vi /tmp/label
.Ed
.Pp
.It
Put the new label on the RAID set:
.Bd -unfilled -offset indent
# disklabel -R raid0 /tmp/label
.Ed
.Pp
.It
Create the file system:
.Bd -unfilled -offset indent
# newfs /dev/rraid0e
.Ed
.Pp
.It
Mount the file system:
.Bd -unfilled -offset indent
# mount /dev/raid0e /mnt
.Ed
.Pp
.It
Use:
.Bd -unfilled -offset indent
# raidctl -c raid0.conf raid0
.Ed
.Pp
to re-configure the RAID set the next time it is needed, or put
raid0.conf into
.Pa /etc
where it will automatically be started by the
.Pa /etc/rc
scripts.
.El
.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
.Em NOT
a substitute for good backup practices.
.Pp
Recomputation of parity
.Em 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.
.Sh FILES
.Bl -tag -width "/etc/raid[0-3].conf" -compact
.It Pa /dev/{,r}raid*
.Cm raid
device special files.
.It Pa /etc/raid[0-3].conf
Files used by
.Xr rc 8
to configure arrays at startup.
.El
.Sh SEE ALSO
.Xr ccd 4 ,
.Xr raid 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
from where it was ported to
.Ox 2.5 .
.Sh BUGS
Hot-spare removal is currently not available.