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metadb


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.

     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  addi-
     tional  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
                     /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 com-
                     mand line in the form, mddbnn, where nn is a
                     two-digit number given to the replica defin-
                     itions.  Refer to the md.tab(4) man page for
                     instructions on setting up replicas 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  initial
                     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 charac-
                     ters  in  front  of  the  device  name  that
                     represent  the status of the state database.
                     Explanations of the characters are displayed
                     following the replica status and are as fol-
                     lows:

                     d                       replica   does   not
                                             have  an  associated
                                             device ID.




                     o                       replica active prior
                                             to  last mddb confi-
                                             guration change



                     u                       replica  is  up   to
                                             date



                     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 ker-
                                             nel



                     m                       replica  is  master,
                                             this    is   replica
                                             selected as input



                     r                       replica   does   not
                                             have  device reloca-
                                             tion information



                     t                       tagged data is asso-
                                             ciated    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  associ-
                                             ated     with    the
                                             replica is not valid




     -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   configurations.
                     "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  nor-
                     mally  used  to  update a newly built system
                     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 argument. 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

     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  metadev-
                                     ice database configuration.



     /kernel/drv/md.conf             Contains  database   replica
                                     information for all metadev-
                                     ices on a system. Also  con-
                                     tains Solaris Volume Manager
                                     configuration information.



EXIT STATUS
     The following exit values are returned:

     0        successful completion



     >0       an error occurred




ATTRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:

     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Availability                | SUNWmdr                     |
    |_____________________________|_____________________________|


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)

     Solaris Volume Manager Administration Guide

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 dev-
          ice










Man pages from Solaris 10 Update 8. See docs.sun.com and www.oracle.com for further documentation and Solaris information.
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