LVM Volume Group Quiesce/Resume

ManualsBrandsHP ManualsSoftwareHP-UX 11i Volume Management (LVM/VxVM) Software

Abstract.............................................................................................................................................. 2

Overview............................................................................................................................................ 3

Commands ......................................................................................................................................... 6

vgchange........................................................................................................................................ 6

Quiescing a volume group - quiescing application reads and writes................................................... 6

Quiescing a volume group - quiescing application writes (allowing reads) .......................................... 6

Resuming normal volume group activity........................................................................................... 6

Automatically resuming a volume group.......................................................................................... 6

vgchgid .......................................................................................................................................... 7

Recommended practices....................................................................................................................... 8

Quiesce the volume group when performing a snapshot or a backup of all the disks in the volume group... 8

Suspend applications and file system activities before quiescing the volume group. ................................. 8

Perform a snapshot or backup of every disk in the volume group. .......................................................... 8

Special considerations for I/O performance sensitive applications......................................................... 8

Sample disk snapshot procedure ........................................................................................................... 9

Determining whether a volume group is quiesced .................................................................................. 10

For more information.......................................................................................................................... 11

Call to action .................................................................................................................................... 11

Summary of content (12 pages)

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LVM Volume Group Quiesce/Resume Abstract.............................................................................................................................................. 2 Overview............................................................................................................................................ 3 Commands ......................................................................................................................................... 6 vgchange..................
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Abstract The LVM volume group Quiesce/Resume feature available on HP-UX 11i v3 allows quiescing reads/writes or just writes to the disks in a volume group to facilitate creating a consistent snapshot of an otherwise active volume group for backup purposes. This feature is designed to work in concert with backup management and disk array management software in order to create a consistent snapshot of the disks that make up an LVM volume group.
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Overview The LVM Quiesce/Resume feature should be used when it is necessary to obtain a stable image of all the disks in an otherwise active volume group. The feature is designed to be used with disk array management or backup management tools to facilitate creating a disk image snapshot copy of the LVM metadata and user data on the disks in the volume group for backup purposes.
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Characteristics of quiesced LVM volume groups The physical volumes in the volume group remain unchanged until the volume group is resumed. Logical volumes may be opened or closed by applications while the volume group is quiesced. Depending upon the quiesce mode specified, application reads and writes or just application writes are quiesced. The corresponding I/O operations are queued and will complete after the volume group is resumed.
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The LVM Quiesce/Resume feature is supported on Serviceguard clusters A volume group activated in shared mode can be quiesced from any node in the cluster and resumed from any node. Invoking the command to quiesce the volume group on any node causes the volume group to be quiesced on all the nodes of the cluster. Likewise resuming the volume group from any node in the cluster will resume it on all the nodes.
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Commands vgchange The vgchange command provides the –Q and –R options to allow quiescing and resuming the volume group: vgchange –Q quiesce_mode [-t quiesce_time] vgname vgchange -R vg_name Quiescing a volume group - quiescing application reads and writes vgchange –Q rw vgname Using the rw quiesce_mode quiesces application reads and writes and LVM metadata updates to the volume group.
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vgchgid The vgchgid command changes the volume group identifier on the disks indicated: vgchgid PhysicalVolumePath [PhysicalVolumePath]... After performing a snapshot of the disks in a volume group, the vgchgid command is used to differentiate the snapshots of the physical volumes from the originals. LVM can then recognize both volume groups (the one with the original physical volumes and the one with the physical volume snapshots) and both volume groups may be activated on the system.
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Recommended practices Quiesce the volume group when performing a snapshot or a backup of all the disks in the volume group. Quiescing the volume group ensures that the LVM metadata and logical volume mirrors are consistent across all the disks in the volume group prior to performing snapshot(s) of the disk(s). Suspend applications and file system activities before quiescing the volume group.
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Sample disk snapshot procedure This is just a sample of what is typically done to create a snapshot image for backup purposes. The actual commands invoked are dependent upon the application and the disk hardware. 1. Flush cached data to disks and/or suspend the applications Some applications do not require any special procedure prior to quiescing the volume group under them.
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Determining whether a volume group is quiesced The vgdisplay and lvdisplay commands indicate the quiesce mode of a quiesced volume group: If a volume group is quiesced the vgdisplay command indicates the quiesce mode as either read/write-quiesced or write-quiesced on the VG Write Access line: vgdisplay vgdata --- Volume groups --VG Name VG Write Access VG Status Max LV Cur LV Open LV Max PV Cur PV Act PV Max PE per PV VGDA PE Size (Mbytes) Total PE Alloc PE Free PE Total PVG Total Spare PVs Total Spare PVs
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For more information To learn more about LVM and HP-UX system administration, refer to the following document on the HP documentation website (http://docs.hp.com): • HP-UX System Administrator's Guide: Logical Volume Management http://docs.hp.com/en/5991-6481/5991-6481.pdf Call to action HP welcomes your input. Please give us comments about this white paper, or suggestions for LVM or related documentation, through our technical documentation feedback website: http://docs.hp.com/en/feedback.
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