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Operating Systems AIX Shared Logical Volume betweem two node on concurrent mode Post 303003767 by hicksd8 on Wednesday 20th of September 2017 07:05:53 AM
Old 09-20-2017
Welcome to the forum.

I'm not an AIX expert so I was hoping that an AIX specialist but I can offer some generic principles on this.

Firstly, you can only ever mount any one filesystem on one server. Only one server can control the superblock (free space table), file locking, and file writing. To have more than one server thinking they could do that is a recipe for instant filesystem corruption.

So there are two common ways to generate the scenario you outline.

Server BD1 can mount the filesystem (like a local drive even though it's a LUN from a SAN), then publish a Network File System (NFS) handle allowing BD2 to mount the same filesystem remotely. Therefore, all I/O to/from the filesystem is going through BD1 which has control. The problem with this "poor man's" solution is that there is no resilience if BD1 goes down.

A "high end" solution would employ a clustering suite. There are many of these available offering different features. In such a configuration each server usually has its own hard IP address and also a virtual IP address that the clients call in on. However, generically speaking, the filesystem is physically connected to both BD1 and BD2 at the same time (via FC, iSCSI, or whatever protocol) with the cluster suite arbitrating which one has control and handles all the I/O. Between BD1 and BD2 there are heartbeats arranged (could be via a serial connection, over IP, or via a file on the SAN) so that one server can detect if the other goes down. In the event of a server failure, the survivor will mount the orphaned filesystems, check them for consistency, switch over the dead server's virtual IP address to itself, and start the applications that the lost server was running. The clients can then continue working within a few short seconds.

Don't be confused by the IBM V3700's capability to remotely mirror a filesystem independently of any host. The V3700 is an entry level enterprise storage device with extreme versatility, BUT, it remains that any filesystem can only be under the control of one host at a time. In some big end systems the filesystems can be controlled (mount, file locking, writing, caching) by the storage controller itself but you are talking very big money.

Hope that helps and that you will get a better answer from an AIX specialist on here.
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Commands Reference, Volume 5, s - u

syncvg_Command

  Purpose

   Synchronizes logical volume copies that are not current.

  Syntax

   syncvg [ -f ] [ -i ] [ -H ] [ -P NumParallelLps ] { -l |
   -p | -v } Name ...

  Description

   The syncvg command synchronizes the physical partitions, which
are copies
   of the original physical partition, that are not current.  The
syncvg
   command can be used with logical volumes, physical volumes, or
volume
   groups, with the Name parameter representing the logical  vol-
ume name,
   physical  volume  name, or volume group name. The synchroniza-
tion process
   can be time consuming, depending on the hardware  characteris-
tics and the
   amount of data.

   When  the  -f flag is used, a good physical copy is chosen and
propagated to
   all other copies of the logical partition, whether or not they
are stale.
   Using this flag is necessary in cases where the logical volume
does not
   have the mirror write consistency recovery.

   Unless disabled, the copies within a volume group are synchro-
nized
   automatically  when the volume group is activated by the vary-
onvg
   command.

   Note:
   For the sycnvg command to be successful,  at  least	one  good
copy of the
   logical  volume should be accessible, and the physical volumes
that
   contains this copy should be in ACTIVE state. If the -f option
is used,
   the above condition applies to all mirror copies.

   If the -P option is not specified, syncvg will check for the
   NUM_PARALLEL_LPS environment variable. The value of NUM_PARAL-
LEL_LPS will
   be used to set the number of logical partitions to be synchro-
nized in
   parallel.

  Flags

		     Specifies a good physical copy is chosen and
propagated
   -f		     to all other copies of  the  logical  parti-
tion, whether or
		     not they are stale.
		     Postpones	writes	for  this volume group on
other active
		     concurrent cluster nodes until this sync op-
eration is
   -H		      complete.  When  using  the -H flag, the -P
flag does not
		     require that all the nodes  on  the  cluster
support the -P
		     flag.  This  flag	is  ignored if the volume
group is not
		     varied on in concurrent mode.
   -i		     Reads the names from standard input.
   -l		     Specifies that the Name parameter represents
a logical
		     volume device name.
   -p		     Specifies that the Name parameter represents
a physical
		     volume device name.
		     Numbers of logical partitions to be synchro-
nized in
		     parallel. The valid range for NumParallelLps
is 1 to 32.
		     NumParallelLps must be tailored to  the  ma-
chine, disks in
		     the volume group, system resources, and vol-
ume group
		     mode.

   -P NumParallelLps When a volume group is varied on in  concur-
rent mode, all
		     other  cluster  nodes  that have this volume
group varied
		     must be at least AIX 4.3.0, otherwise syncvg
will ignore
		     this option and continue.

		     Note:
		     See Description above for more information.
   -v		     Specifies that the Name parameter represents
a volume
		     group device name.

  Examples

    1. To synchronize the copies on physical volumes hdisk04  and
hdisk05,
       enter:

	 syncvg
 -p hdisk04 hdisk05

    2.	To synchronize the copies on volume groups vg04 and vg05,
enter:

	 syncvg
 -v vg04 vg05

  Files

   /usr/sbin/syncvg Contains the syncvg command.
   /tmp 	     Directory	where  the  temporary  files  are
stored and while
		    the command is running.

  Related Information

   The varyonvg command.

   The Logical volumn storage in Operating system and device man-
agement
   explains the Logical Volume Manager, physical volumes, logical
volumes,
   volume  groups, organization, ensuring data integrity, and al-
location
   characteristics.

   The System management interface tool in Operating  system  and
device
   management  explains the structure, main menus, and tasks that
are done
   with SMIT.

________________________________________________________________________________

		      Commands Reference, Volume 5, s - u

syncvg_Command

  Purpose

   Synchronizes logical volume copies that are not current.

  Syntax

   syncvg [ -f ] [ -i ] [ -H ] [ -P NumParallelLps ] { -l |
   -p | -v } Name ...

  Description

   The syncvg command synchronizes the physical partitions, which
are copies
   of the original physical partition, that are not current.  The
syncvg
   command can be used with logical volumes, physical volumes, or
volume
   groups, with the Name parameter representing the logical  vol-
ume name,
   physical  volume  name, or volume group name. The synchroniza-
tion process
   can be time consuming, depending on the hardware  characteris-
tics and the
   amount of data.

   When  the  -f flag is used, a good physical copy is chosen and
propagated to
   all other copies of the logical partition, whether or not they
are stale.
   Using this flag is necessary in cases where the logical volume
does not
   have the mirror write consistency recovery.

   Unless disabled, the copies within a volume group are synchro-
nized
   automatically  when the volume group is activated by the vary-
onvg
   command.

   Note:
   For the sycnvg command to be successful,  at  least	one  good
copy of the
   logical  volume should be accessible, and the physical volumes
that
   contains this copy should be in ACTIVE state. If the -f option
is used,
   the above condition applies to all mirror copies.

   If the -P option is not specified, syncvg will check for the
   NUM_PARALLEL_LPS environment variable. The value of NUM_PARAL-
LEL_LPS will
   be used to set the number of logical partitions to be synchro-
nized in
   parallel.

  Flags

		     Specifies a good physical copy is chosen and
propagated
   -f		     to all other copies of  the  logical  parti-
tion, whether or
		     not they are stale.
		     Postpones	writes	for  this volume group on
other active
		     concurrent cluster nodes until this sync op-
eration is
   -H		      complete.  When  using  the -H flag, the -P
flag does not
		     require that all the nodes  on  the  cluster
support the -P
		     flag.  This  flag	is  ignored if the volume
group is not
		     varied on in concurrent mode.
   -i		     Reads the names from standard input.
   -l		     Specifies that the Name parameter represents
a logical
		     volume device name.
   -p		     Specifies that the Name parameter represents
a physical
		     volume device name.
		     Numbers of logical partitions to be synchro-
nized in
		     parallel. The valid range for NumParallelLps
is 1 to 32.
		     NumParallelLps must be tailored to  the  ma-
chine, disks in
		     the volume group, system resources, and vol-
ume group
		     mode.

   -P NumParallelLps When a volume group is varied on in  concur-
rent mode, all
		     other  cluster  nodes  that have this volume
group varied
		     must be at least AIX 4.3.0, otherwise syncvg
will ignore
		     this option and continue.

		     Note:
		     See Description above for more information.
   -v		     Specifies that the Name parameter represents
a volume
		     group device name.

  Examples

    1. To synchronize the copies on physical volumes hdisk04  and
hdisk05,
       enter:

	 syncvg
 -p hdisk04 hdisk05

    2.	To synchronize the copies on volume groups vg04 and vg05,
enter:

	 syncvg
 -v vg04 vg05

  Files

   /usr/sbin/syncvg Contains the syncvg command.
   /tmp 	     Directory	where  the  temporary  files  are
stored and while
		    the command is running.

  Related Information

   The varyonvg command.

   The Logical volumn storage in Operating system and device man-
agement
   explains the Logical Volume Manager, physical volumes, logical
volumes,
   volume  groups, organization, ensuring data integrity, and al-
location
   characteristics.

   The System management interface tool in Operating  system  and
device
   management  explains the structure, main menus, and tasks that
are done
   with SMIT.
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