vxplex

NAME

vxplex - perform VERITAS Volume Manager operations on plexes

SYNOPSIS

DESCRIPTION

The vxplex utility performs VERITAS Volume Manager (VxVM) operations on plexes and on volume-and-plex combinations. The first operand is a keyword that determines the specific operation to perform. The remaining operands specify the configuration objects to which the operation is to be applied.

Each operation can be applied to only one disk group at a time. Any volume or plex operands are used to determine a default disk group, according to the standard disk group selection rules described in vxintro(1M). A specific disk group can be forced with -g diskgroup.

KEYWORDS

att

Attaches each named plex to the named volume. This can be applied to dissociated plexes, or to non-enabled plexes already associated with the named volume. If the volume is enabled, then the result of the successful operation is to associate the plex (if needed) and to recover the plex to have the same contents as all other attached plexes in the volume. The rules for performing the attach depend upon the usage type of the named volume.

Attaching a plex is the normal means of recovering a plex after a disk replacement, or after a plex offline.

By default, the FastResync feature (if licensed) is used to speed up the synchronization of re-attached plexes. This behavior can be changed by defining a value for the usefmr attribute in the vxplex defaults file, /etc/default/vxplex.

If a valid license for the FastResync feature exists on the system, vxplex uses this feature under the following conditions:

• If a defaults file does not exist.
• If a defaults file exists, but no value is defined for the usefmr attribute.
• If a defaults file exists, and contains the entry usefmr=yes.

If a valid FastResync license is not found, or the defaults file contains the entry usefmr=no, FastResync is not used and a full resynchronization is performed.

A different defaults file can be specified by using the -d option. See the description in the OPTIONS section for details.

convert

Converts a snapshot plex into a regular plex, or a regular plex into a snapshot plex. This operation allows you to create a snapshot plex for a volume that already has two or more mirrors without using snapstart.

The main difference between a snapshot plex and a regular plex is the plex state. A plex may be in one of many states depending on errors, detaches and other transactions. The vxplex convert operation is limited to moving plexes between the ACTIVE, SNAPDONE, and SNAPDIS plex states. The state of a regular plex that is attached to an open volume is ACTIVE. The state of a snapshot plex after the snapshot operation has completed is usually SNAPDONE, although it may be in the SNAPDIS state if attached using vxplex.

The state attribute to the convert operation specifies the final state of the plex after conversion: ACTIVE, SNAPDIS, or SNAPDONE. A regular plex is usually converted to a snapshot plex in the SNAPDONE state, and a snapshot plex is usually converted to a regular plex in the ACTIVE state. The SNAPDIS option is provided for convenience of scripting.

As well as changing the plex state, the convert operation also changes the I/O mode and the noerror flag for the plex. The I/O mode is set to read/write for a regular plex, and to read-only for a snapshot plex. The noerror flag is cleared for regular plexes, and set for snapshot plexes. Additionally, if Persistent FastResync is enabled on a volume (that is, a data change object (DCO) and DCO volume are associated with the volume), a DCO plex must be added if a regular plex is converted to a snapshot plex, and a DCO plex must be removed if a snapshot plex is converted to a regular plex.

The following example shows how to convert the regular plex plex1 to a snapshot plex, which is associated with the DCO plex, dcoplex1:


vxplex -g mydg -o dcoplex=dcoplex1 convert state=SNAPDONE plex1

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  Note    The last complete regular plex in a volume, an incomplete regular plex, or a dirty region logging (DRL) log plex cannot be converted into a snapshot plex.

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  Note    This discussion applies only to traditional third-mirror snapshots. It does not apply to full-sized instant snapshots that are created and administered using the vxsnap command. Plexes that are broken off for use in instant snapshots must be in the ACTIVE and not the SNAPDONE state.

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cp

Copies the named volume to the named plexes. The volume must be enabled, and the named plexes must not be associated. The result of the operation is a set of dissociated plexes that is an exact copy of the volume at the time of completion of the operation. The rules for performing the attach depend upon the usage type of the named volume. To improve the quality of the copies, some usage types attempt to make the detached plex consistent with respect to in-memory data.

This operation can be used to make a copy of a volume, for backup purposes, without mirroring the volume in advance.

det

Detaches each of the named plexes. Detaching a plex leaves the plex associated with its volume, but prevents normal volume I/O from being directed to the plex. This operation can be applied to plexes that are enabled or disabled. The rules for performing the detach depend upon the usage types of the volumes involved. The operation does not apply to dissociated plexes.

dis

Dissociates each of the named plexes. Dissociating a plex breaks the link between the plex and its volume. A dissociated plex is inaccessible until it is reassociated, which can be done either with vxplex att or with vxmake. Any checks and synchronizations that apply to the det operation also apply to the dis operation.

Plex dissociation is the typical means of unmirroring a volume or reducing the mirror count for a volume. To do this, use -o rm to dissociate and remove the plex (and its associated subdisks) in the same operation. This makes the space used by those subdisks usable for new allocations (such as with vxassist or vxmake).

Plex dissociation can also be used for file system backups of volumes that are normally mirrored. Plex devices are not directly mountable, so the backup method described for the det operation does not work if the backup program requires a mounted file system. To support such backup programs, a plex can be dissociated and can then be allocated to a new volume as in the following example:


vxmake -U gen vol volume01 plex=plex01

The created volume can then be started and mounted for use by the backup program.

Another common use of dis is to remove DCM plexes from data volumes. Removing all the DCMs from a single data volume disables SRL overflow protection for all the data volumes in the RVG. The dissociation fails if the DCM is active.

You can also remove a mirror from a volume, as shown in the following example:


vxplex -o rm dis vol01-02

mv

Attach the plex newplex to the volume that oldplex is associated with and dissociate oldplex. The volume cannot be disabled, and newplex must name a dissociated plex. The operation ensures seamless replacement of the dissociated plex without loss of data in the volume and without significant delays in volume accessibility.

A primary purpose for the plex move operation is to move a plex that is using a disk to another location. In support of this purpose for the operation, -o rm can be specified to remove the original plex after completion of the operation.

For concatenated or striped plexes, the vxsd mv operation can be used to move individual subdisks off a disk. The rules for performing the move depend upon the usage types of the volume to which oldplex is associated.

oem

Not used in this release.

snapabort

This operation can be used in order to cancel the effects of a snapstart.

snapstart and snapshot

These two operations form the two parts of a preferred means of copying a volume to a plex for backup purposes. The snapstart operation attaches a plex to a volume and, when the operation is complete, leaves the plex associated as a temporary plex.

If the -s option is used to specify one or more source plexes, snapstart synchronizes the data in the newly attached snapshot plex from the source plexes.

If you use snapstart to attach a pre-existing plex, run the following command to convert the state of the plex to SNAPDONE when the snapstart operation is complete:


vxplex -g diskgroup convert state=SNAPDONE plex

After the snapstart operation completes and the temporary plex is in the SNAPDONE state, you can use vxplex snapshot to convert it into a new volume. If identical new_volume names are specified for two or more SNAPDONE plexes, a mirrored snapshot volume is created.

For convenience of administration, you can use the -o comment=comment option with snapshot to define a comment for the snapshot volume.

To improve the quality of the copies, some usage types attempt to make the detached plex consistent with respect to in-memory data.

This method of backup is preferable to using vxplex cp because it allows you to coordinate breaking off the plex from the original volume at a well-defined point in time. This is important, since attaching a plex to a volume can take a considerable amount of time, and it is difficult to know when it will complete. Also, directly converting the plex into a new volume is more convenient than requiring additional steps.

snapback

This operation dissociates one or more named plexes from their current volume and attaches them to the specified volume. If a plex is the last in its current volume, this volume is removed from the disk group.

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  Note    The volumes containing the named plexes and destination volume must be in the same disk group.

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OPTIONS

-c checkpoint

Sets a named checkpoint on a snapshot. Note: This option is a deprecated feature of VVR and should not be used.

-d defaults_file

Specifies the absolute pathname of a defaults file to use instead of /etc/default/vxplex. The value that is assigned to the usefmr attribute in the defaults file defines whether or not vxplex should attempts to use the FastResync feature when re-attaching a plex.

vxplex fails with an error if the defaults file specified to the -d option does not exist.

See the description of the att command for more details.

-f

Forces an operation that VxVM considers potentially dangerous or of questionable use. This permits a limited set of operations that would otherwise be disallowed. Some operations may be disallowed even with this flag.

-g diskgroup

Specifies the disk group for the operation, either by disk group ID or by disk group name. By default, the disk group is chosen based on the name operands.

-o useopt

Passes in usage-type-specific options to the operation. A certain set of operations are expected to be implemented by all usage types:

comment=comment

Sets a comment on a snapshot volume during a snapshot operation.

dcoplex=dco_plex

Specifies the DCO plex to be used with a convert operation.

iosize=size

Performs copy operations in regions with the length specified by size, which is a standard VERITAS Volume Manager length number (see vxintro(1M)). Specifying a larger number typically causes the operation to complete sooner, but with greater impact on other processes using the volume. The default I/O size is 1 megabyte.

noecopy

Turns off Extended Copy Services for one invocation of an cp, mv or snapstart operation. By default, the Extended Copy Services feature of VxVM automatically offloads copy requests to an array's copy manager if both the source and destination disks are enabled for ecopy operations.

nofmr

Forces a full resynchronization during a snapback or att operation even if FastResync is enabled.

numchild=number

Specifies the number of child processes that are used to perform resynchronization during att and snapback operations. The default value of number is 1 (no child processes), which is the same as specifying a number of 0. Specifying a larger value for number potentially speeds up resynchronization, although the effectiveness of this depends to some extent on the underlying characteristics of the disk array. No further benefit in performance may be noticeable for a value for number greater than 3.

By default, the child processes divide the volume into equally sized chunks, which they then resynchronize independently with the volume. This behavior may be modified using the useopt sequential.

renamesnapplex

Specifies that a snapshot plex is renamed when the snapshot operation is used to create a snapshot volume. If this option is not specified, the plex retains the same name that it had in the original volume.

resyncfromoriginal

Chooses the original volume as the preferred copy of data during a snapback or att operation. This is the default behavior.

resyncfromreplica

Chooses the replica plex as the preferred copy of data during a snapback or att operation. resyncfromoriginal is the default behavior.

rm

Removes the plexes after successful completion of a vxplex dis operation. Remove the source plex after successful completion of vxplex mv.

sequential

When specified with the useopt numchild for values of number greater than 1, the child processes co-operate in resynchronizing regions of the volume that are close together, starting at the beginning of the volume and moving to the end. This creates more overhead for the resynchronization, but it potentially makes better use of the sequential read-ahead buffer of the physical disks.

slow[=iodelay]

Reduces the system performance impact of copy operations. Such operations are usually performed on small regions of the volume (normally from 16 kilobytes to 128 kilobytes). This option inserts a delay between the recovery of each such region. A specific delay can be specified with iodelay as a number of milliseconds; otherwise, a default is chosen (normally 250 milliseconds).

-R request_portal

Specifies a rendezvous file path name for regular configuration and query requests. /etc/vx/vold_request is the default.

-s srcplex1 [-s srcplex2] ...

Specifies one or more source plexes to be used for resynchronization in the att and snapstart operations.

-t tasktag

If any tasks are registered to track the progress of the operation, marks them with the tag tasktag. The tag specified by tasktag is a sequence of up to 16 alphanumeric characters.

-T taskid

Associates new tasks with the specified parent task ID.

-U usetype

Limits the operation to apply to this usage type. Attempts to affect volumes with a different usage type fail.

-v volume

Requires that the plex named by a plex or oldplex operand be associated with the named volume. This option can be used as a sanity check, to ensure that the specified plex is actually the plex desired for the operation.

-V

Displays a list of utilities that would be called from vxplex, along with the arguments that would be passed. The -V option performs a preview run so the utilities are not actually called.

FSGEN AND GEN USAGE TYPES

The fsgen and gen usage types provide similar, though not identical, semantics for all operations of the vxplex utility. In particular, the fsgen usage type attempts to flush in-memory data cached for the file system residing on the volume. For most file systems, this consists of calling sync(1M) to attempt to flush all in-memory data to disk. For the vxfs file system type, special ioctls are called to ensure a reliable flush of the involved volume.

If a vxplex operation is interrupted by a signal, then an attempt is made to restore the disk group configuration to a state that is roughly equivalent to its original state. If this attempt is interrupted (such as through another signal) then the user may need to perform some cleanup. The specific cleanup actions that are needed are written to the standard error before vxplex exits.

The fsgen and gen usage types provide the following options as arguments to -o in addition to the required options:

force

Forces an operation that VxVM considers potentially dangerous or of questionable use. This applies to attempts to detach or dissociate the last (complete) plex in a volume, or to attempts to move a plex to a plex that has a different size. This flag is the same as -f.

mapzero

If a plex is moved to a new plex that has regions that are mapped to a subdisk in the destination, but are not mapped to a subdisk for any enabled, readable plex in the volume, then zero out that mapped region in the destination plex. Without this flag, the mapped region may be left unchanged from its original contents.

rerr

Ignore volume or plex read errors when copying data onto a plex. A warning message is written to standard error if a read error occurs, but the error does not affect success of the operation. This operation can be used only with the cp operation; the operation is ignored if used with other operations.

werr

Ignore plex write errors when copying data onto a plex. A warning message is written to standard error if a write error occurs, but the error does not affect success of the operation. This operation can be used only with the cp operation; the operation is ignored if used with other operations.

Limitations and extensions for the fsgen and gen usage types consist of the following:

att

If the volume is enabled and one of the named plexes is associated with the volume, then the plex must be STALE, EMPTY, ACTIVE, or OFFLINE. If the operation succeeds in attaching a plex, then any I/O fail condition for the plex is cleared. Also, attaching to an enabled volume requires that the volume have at least one enabled, read-write plex.

If the volume is not enabled, then the named plexes are associated with the volume (if not already associated) and are set to the STALE state, so that the plex is fully attached by the next vxvol start or vxvol startall operation that is applied to the volume.

If the log type of the volume is UNDEF and an unassociated plex with a log subdisk is attached, the volume is automatically converted to have a log type of DRL. Logging of volume changes is enabled when the volume has at least one enabled, associated plex with an enabled log subdisk and at least two read-write mode plexes.

An attempt to attach an unassociated plex fails if the putil0 field is not empty. This makes it possible to prevent use of a plex by using vxedit set to set the putil0 field to a non-empty string. The putil0 field can then be cleared with either vxedit set or with vxmend clear putil0.

cp

The fsgen and gen usage types do not add any specific restrictions to the cp operation.

det, dis

A detach or dissociate of a plex can fail for one of two reasons. In an enabled volume a detach or dissociate fails if applied to a plex that is the last complete, enabled, read-write plex in the volume and the volume contains two or more non-complete, enabled, read-write plexes. In other words, a volume cannot be left with two enabled, non-complete plexes. A complete plex is one that is at least as long as the volume, and has subdisks mapped to the plex for all blocks up to the length of the volume. The -f option is required to reduce a volume to containing one enabled, read-write, non-complete plex, or to having no enabled, read-write plexes at all. The other way a detach or dissociate can fail is if the plex is of type DCM and it is active. A DCM is active if SRL overflow protection is active or if a resync of a replicated volume is in progress.

The det operation changes the state for an ACTIVE or CLEAN plex to STALE. The next time the volume is started, the plex is re-attached automatically.

mv

If the destination plex has unmapped regions (a range of blocks in the plex with no backing subdisk) that are not mapped in the source plex, or if the destination plex is shorter than the source plex, then the -f option is required. Even with -f, the operation prevents the plex from being sparsed such that the volume would be left with two or more sparse, enabled, read-write plexes, but no complete plexes.

RAID5 USAGE-TYPE

The raid5 usage type provides the following options as arguments to -o in addition to the required options:

force

Forces an operation that VxVM considers potentially dangerous or of questionable use. This applies to attempts to dissociate the RAID-5 plex of a non-EMPTY volume or to remove the last RAID-5 log plex of a non-EMPTY volume.

As with other usage types, if a vxplex operation is interrupted by a signal, then an attempt is made to restore the disk group configuration to a state that is roughly equivalent to its original state. If this attempt is interrupted (such as through another signal) then the user may need to perform some cleanup. The specific cleanup actions that are needed are written to the standard error before vxplex exits.

The raid5 usage type supports the following keywords as described here:

att

Attaches the named plexes to the named volume. If a plex has a layout of RAID, the plex is attached as the RAID-5 plex of the RAID-5 volume. To attach a RAID-5 plex to the volume, the volume must be disabled and be in the EMPTY state, and the RAID-5 plex is given a state of EMPTY.

If a plex has a layout other than RAID, the plex is attached as a RAID-5 log plex for the RAID-5 volume. If the volume has no RAID-5 log plexes, the log length for the volume is set to the length of the smallest log plex being attached. If the volume already has at least one log plex, a plex can only be attached as a log plex if its contiguous length is at minimum the volume's log length. RAID-5 log plexes cannot be sparse in respect to the volume's log length; attempts to attach a sparse log plex fail.

If the RAID-5 volume is not enabled, log plexes are attached and marked as STALE. If the RAID-5 volume is enabled and has no log plexes, attaching a log plex causes plexes being attached as log plexes to be zeroed before they are enabled. Otherwise, the new log plexes are attached write-only and the contents of the existing log plexes are copied to the new log plexes using ATOMIC_COPY ioctls, after which the logs are enabled.

dis

Dissociates the named plex from the RAID-5 volume to which it is attached. If the plex is the RAID-5 plex of the volume and the volume is not EMPTY, this requires the -o force option, as any data on the volume would be lost. If the plex is a log plex for the volume and would leave the RAID-5 volume with no usable log plexes, the -o force option is required.

FILES

/etc/default/vxplex

Standard defaults file that can be used to determine whether FastResync is used when attaching plexes. An alternative defaults file may be specified by using the -d option.

/usr/lib/vxvm/type/usetype/vxplex

The utility that performs vxplex operations for a particular volume usage type.

/usr/lib/vxvm/type/fsgen/fs.d/fstype/vxsync

Path to a program used with the fsgen usage type for synchronizing in-memory file system data with a volume, for the file system type fstype. The program is given arguments of a volume name and one or more plex names. For the vxfs file system type, this program uses the VERITAS File System (VxFS) freeze feature to ensure a perfect synchronized detach.

EXIT CODES

The vxplex utility exits with a non-zero status if the attempted operation fails. A non-zero exit code is not a complete indicator of the problems encountered but rather denotes the first condition that prevented further execution of the utility.

See vxintro(1M) for a list of standard exit codes.

EXAMPLES

Associate plex vol02-03 with the existing volume vol02:

Temporarily detach plex vol03-03 from its volume:

Dissociate plex vol01-03 from the plexes vol01-01 through vol01-03 on volume vol01:

SEE ALSO

sync(1M), vxassist (1M), vxedit (1M), vxintro (1M), vxmend (1M), vxsnap (1M), vxtask (1M), vxvol (1M)