System Administration Commands metadb(1M)
NAME
metadb - create and delete replicas of the metadevice state
database
SYNOPSIS
/sbin/metadb -h
/sbin/metadb [-s setname]
/sbin/metadb [-s setname] -a [-f] [-k system-file] mddbnn
/sbin/metadb [-s setname] -a [-f] [-k system-file]
[-c number] [-l length] slice...
/sbin/metadb [-s setname] -d [-f] [-k system-file] mddbnn
/sbin/metadb [-s setname] -d [-f] [-k system-file] slice...
/sbin/metadb [-s setname] -i
/sbin/metadb [-s setname] -p [-k system-file]
[mddb.cf-file]
DESCRIPTION
The metadb command creates and deletes replicas of the meta-
device state database. State database replicas can be
created on dedicated slices, or on slices that will later
become part of a simple metadevice (concatenation or stripe)
or RAID5 metadevice. Do not place state database replicas on
fabric-attached storage, SANs, or other storage that is not
directly attached to the system and available at the same
point in the boot process as traditional SCSI or IDE drives.
See NOTES.
The metadevice state database contains the configuration of
all metadevices and hot spare pools in the system. Addition-
ally, the metadevice state database keeps track of the
current state of metadevices and hot spare pools, and their
components. Solaris Volume Manager automatically updates the
metadevice state database when a configuration or state
change occurs. A submirror failure is an example of a state
change. Creating a new metadevice is an example of a confi-
guration change.
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System Administration Commands metadb(1M)
The metadevice state database is actually a collection of
multiple, replicated database copies. Each copy, referred to
as a replica, is subject to strict consistency checking to
ensure correctness.
Replicated databases have an inherent problem in determining
which database has valid and correct data. To solve this
problem, Volume Manager uses a majority consensus algorithm.
This algorithm requires that a majority of the database
replicas be available before any of them are declared valid.
This algorithm strongly encourages the presence of at least
three initial replicas, which you create. A consensus can
then be reached as long as at least two of the three repli-
cas are available. If there is only one replica and the sys-
tem crashes, it is possible that all metadevice configura-
tion data can be lost.
The majority consensus algorithm is conservative in the
sense that it will fail if a majority consensus cannot be
reached, even if one replica actually does contain the most
up-to-date data. This approach guarantees that stale data
will not be accidentally used, regardless of the failure
scenario. The majority consensus algorithm accounts for the
following: the system will stay running with exactly half or
more replicas; the system will panic when less than half the
replicas are available; the system will not reboot without
one more than half the total replicas.
When used with no options, the metadb command gives a short
form of the status of the metadevice state database. Use
metadb -i for an explanation of the flags field in the out-
put.
The initial state database is created using the metadb com-
mand with both the -a and -f options, followed by the slice
where the replica is to reside. The -a option specifies that
a replica (in this case, the initial) state database should
be created. The -f option forces the creation to occur, even
though a state database does not exist. (The -a and -f
options should be used together only when no state databases
exist.)
Additional replicas beyond those initially created can be
added to the system. They contain the same information as
the existing replicas, and help to prevent the loss of the
configuration information. Loss of the configuration makes
operation of the metadevices impossible. To create
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System Administration Commands metadb(1M)
additional replicas, use the metadb -a command, followed by
the name of the new slice(s) where the replicas will reside.
All replicas that are located on the same slice must be
created at the same time.
To delete all replicas that are located on the same slice,
the metadb -d command is used, followed by the slice name.
When used with the -i option, metadb displays the status of
the metadevice state databases. The status can change if a
hardware failure occurs or when state databases have been
added or deleted.
To fix a replica in an error state, delete the replica and
add it back again.
The metadevice state database (mddb) also contains a list of
the replica locations for this set (local or shared
diskset).
The local set mddb can also contain host and drive informa-
tion for each of the shared disksets of which this node is a
member. Other than the diskset host and drive information
stored in the local set mddb, the local and shared diskset
mddbs are functionality identical.
The mddbs are written to during the resync of a mirror or
during a component failure or configuration change. A confi-
guration change or failure can also occur on a single
replica (removal of a mddb or a failed disk) and this causes
the other replicas to be updated with this failure informa-
tion.
OPTIONS
Root privileges are required for all of the following
options except -h and -i.
The following options can be used with the metadb command.
Not all the options are compatible on the same command line.
Refer to the SYNOPSIS to see the supported use of the
options.
-a Attach a new database device. The
/kernel/drv/md.conf file is automatically
updated with the new information and the
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System Administration Commands metadb(1M)
/etc/lvm/mddb.cf file is updated as well.
An alternate way to create replicas is by
defining them in the /etc/lvm/md.tab file
and specifying the assigned name at the
command line in the form, mddbnn, where nn
is a two-digit number given to the replica
definitions. Refer to the md.tab(4) man
page for instructions on setting up repli-
cas in that file.
-c number Specifies the number of replicas to be
placed on each device. The default number
of replicas is 1.
-d Deletes all replicas that are located on
the specified slice. The
/kernel/drv/md.conf file is automatically
updated with the new information and the
/etc/lvm/mddb.cf file is updated as well.
-f The -f option is used to create the ini-
tial state database. It is also used to
force the deletion of replicas below the
minimum of one. (The -a and -f options
should be used together only when no state
databases exist.)
-h Displays a usage message.
-i Inquire about the status of the replicas.
The output of the -i option includes char-
acters in front of the device name that
represent the status of the state data-
base. Explanations of the characters are
displayed following the replica status and
are as follows:
d replica does not have an associated
device ID.
o replica active prior to last mddb
configuration change
u replica is up to date
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l locator for this replica was read
successfully
c replica's location was in
/etc/lvm/mddb.cf
p replica's location was patched in
kernel
m replica is master, this is replica
selected as input
r replica does not have device reloca-
tion information
t tagged data is associated with the
replica
W replica has device write errors
a replica is active, commits are occur-
ring to this
M replica had problem with master
blocks
D replica had problem with data blocks
F replica had format problems
S replica is too small to hold current
database
R replica had device read errors
B tagged data associated with the
replica is not valid
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-k system-file Specifies the name of the kernel file
where the replica information should be
written. The default system-file is
/kernel/drv/md.conf. This option is for
use with the local diskset only.
-l length Specifies the size of each replica. The
default length is 8192 blocks, which
should be appropriate for most configura-
tions. "Replica" sizes of less than 128
blocks are not recommended.
-p Specifies updating the system file
(/kernel/drv/md.conf) with entries from
the /etc/lvm/mddb.cf file. This option is
normally used to update a newly built sys-
tem before it is booted for the first
time. If the system has been built on a
system other than the one where it will
run, the location of the mddb.cf on the
local machine can be passed as an argu-
ment. The system file to be updated can be
changed using the -k option. This option
is for use with the local diskset only.
-s setname Specifies the name of the diskset on which
the metadb command will work. Using the -s
option will cause the command to perform
its administrative function within the
specified diskset. Without this option,
the command will perform its function on
local database replicas.
slice Specifies the logical name of the physical
slice (partition), such as
/dev/dsk/c0t0d0s3.
EXAMPLES
Example 1 Creating Initial State Database Replicas
The following example creates the initial state database
replicas on a new system.
# metadb -a -f c0t0d0s7 c0t1d0s3 c1t0d0s7 c1t1d0s3
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System Administration Commands metadb(1M)
The -a and -f options force the creation of the initial
database and replicas. You could then create metadevices
with these same slices, making efficient use of the system.
Example 2 Adding Two Replicas on Two New Disks
This example shows how to add two replicas on two new disks
that have been connected to a system currently running
Volume Manager.
# metadb -a c0t2d0s3 c1t1d0s3
Example 3 Deleting Two Replicas
This example shows how to delete two replicas from the sys-
tem. Assume that replicas have been set up on
/dev/dsk/c0t2d0s3 and /dev/dsk/c1t1d0s3.
# metadb -d c0t2d0s3 c1t1d0s3
Although you can delete all replicas, you should never do so
while metadevices still exist. Removing all replicas causes
existing metadevices to become inoperable.
FILES
/etc/lvm/mddb.cf Contains the location of each copy of
the metadevice state database.
/etc/lvm/md.tab Workspace file for metadevice data-
base configuration.
/kernel/drv/md.conf Contains database replica information
for all metadevices on a system. Also
contains Solaris Volume Manager con-
figuration information.
EXIT STATUS
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The following exit values are returned:
0 successful completion
>0 an error occurred
ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
ATRIBUTE TYPE ATRIBUTE VALUE
Availability SUNWmdr
Interface Stability Stable
SEE ALSO
mdmonitord(1M), metaclear(1M), metadetach(1M), metahs(1M),
metainit(1M), metaoffline(1M), metaonline(1M),
metaparam(1M), metarecover(1M), metarename(1M),
metareplace(1M), metaroot(1M), metaset(1M), metassist(1M),
metastat(1M), metasync(1M), metattach(1M), md.tab(4),
md.cf(4), mddb.cf(4), md.tab(4), attributes(5), md(7D)
NOTES
Replicas cannot be stored on fabric-attached storage, SANs,
or other storage that is not directly attached to the sys-
tem. Replicas must be on storage that is available at the
same point in the boot process as traditional SCSI or IDE
drives. A replica can be stored on a:
o Dedicated local disk partition
o Local partition that will be part of a volume
o Local partition that will be part of a UFS logging
device
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