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Top Forums UNIX for Beginners Questions & Answers Should I use a CoW filesystem on my PC if I only wanted snapshot capabilities ? Post 303044797 by stomp on Wednesday 4th of March 2020 05:42:58 AM
Old 03-04-2020
Another comment:

A con against zfs is the inability to remove VDEVs. A VDEV is a subpart of a volume.

Example:

Say you have a data volume consisting of a single disk(=vdev, 1 TB). You decide to replace your vdev of a single disk with a raid-1 vdev(1 TB), since you want add redundancy to be safe in case of a disk crash. That's possible. Over the years, you add another 2 vdevs(2x2TB,2x4TB) with raid-1 arrays. So you then have 3 vdevs making up your volume consisting of 2 disks each with an overall capacity of 7 TB.

You now decide you want to increase your storage again and simultaneously reorganize your 3 x raid1(6 disks=>7 TB usable) to 1 x raidz2(5x6 TB =>18 TB usable) to be able to cope with more simulateous disk crashes(2 disk crashes without data loss here) and at the same time reduce the number of active disks(6->5).

With zfs this is only possible by reformatting, since device removal is not fully supported by now. So you have to copy all the data, which must be done offline. ZFS top level device removal is in development at the moment, but i expect some years to pass until even raidz vdevs can be removed.

With LVM you can just add the new underlying disks and remove the old disks. No problem. All is possible to be done online. Btrfs can do that to and is even flexible to do more advanced migrations.

And Here are some experience reports about btrfs and zfs from users:

ZFS Vs BTRFS : linux

Some not to long gone data loss stories about btrfs are also there. I assume the cause may be lacking knowledge about file system operation. But of course that's only a suspicion.

Last edited by stomp; 03-04-2020 at 06:52 AM..
 

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vgmove(1M)																vgmove(1M)

NAME
vgmove - move data from an old set of disks in a volume group to a new set of disks SYNOPSIS
autobackup] diskmapfile vg_name autobackup] diskfile diskmapfile vg_name DESCRIPTION
The command migrates data from the existing set of disks in a volume group to a new set of disks. After the command completes successfully, the new set of disks will belong to the same volume group. The command is intended to migrate data on a volume group from old storage to new storage. The diskmapfile specifies the list of source disks to move data from, and the list of destination disks to move data to. The user may choose to list only a subset of the existing physical volumes in the volume group that need to be migrated to a new set of disks. The format of the diskmapfile file is shown below: source_pv_1 destination_pv_1_1 destination_pv_1_2 .... source_pv_2 destination_pv_2_1 destination_pv_2_2 .... .... source_pv_n destination_pv_n_1 destination_pv_n_2 .... If a destination disk is not already part of the volume group, it will be added using see vgextend(1M). Upon successful completion of the source disk will be automatically removed from the volume group using see vgreduce(1M). After successful migration, the destination disks are added to the LVM configuration files; namely, or The source disks along with their alternate links are removed from the LVM configuration files. A sample diskmapfile is shown below: /dev/disk/disk1 /dev/disk/disk51 /dev/disk/disk52 /dev/disk/disk2 /dev/disk/disk51 /dev/disk/disk3 /dev/disk/disk53 The diskmapfile can be manually created, or it can be automatically generated using the diskfile and diskmapfile options. The argument diskfile contains a list of destination disks, one per line such as the sample file below: /dev/disk/disk51 /dev/disk/disk52 /dev/disk/disk53 When the option is given, reads a list of destination disks from diskfile, generates the source to destination mapping, and saves it to diskmapfile. The volume group must be activated before running the command. If the command is interrupted before it completes, the volume group is in the same state it was at the beginning of the command. The migration can be continued by running the command with the same options and disk mapping file. Options and Arguments The command recognizes the following options and arguments: vg_name The path name of the volume group. Set automatic backup for this invocation of autobackup can have one of the following values: Automatically back up configuration changes made to the volume group. This is the default. After this command executes, the command is executed for the volume group; see vgcfgbackup(1M). Do not back up configuration changes this time. Specify the name of the file containing the source to destination disk mapping. If the option is also given, will generate the disk mapping and save it to this filename. (Note that if the diskmapfile already exists, the file will be overwritten). Otherwise, will perform the data migration using this diskmapfile. Specify the name of the file containing the list of destination disks. This option is used with the option to generate the diskmapfile. When the option is used, no volume group data is moved. Preview the actions to be taken but do not move any volume group data. Shared Volume Group Considerations For volume group version 1.0 and 2.0, cannot be used if the volume group is activated in shared mode. For volume groups version 2.1 (or higher), can be performed when activated in either shared, exclusive, or standalone mode. Note that the daemon must be running on all the nodes sharing a volume group activated in shared mode. See lvmpud(1M). When a node wants to share the volume group, the user must first execute a if physical volumes were moved in or out of the volume group at the time the volume group was not activated on that node. LVM shared mode is currently only available in Serviceguard clusters. EXTERNAL INFLUENCES
Environment Variables determines the language in which messages are displayed. If is not specified or is null, it defaults to "C" (see lang(5)). If any internationalization variable contains an invalid setting, all internationalization variables default to "C" (see environ(5)). EXAMPLES
Move data in volume group from to After the migration, remove from the volume group: Generate a source to destination disk map file for where the destination disks are and SEE ALSO
lvmpud(1M), pvmove(1M), vgcfgbackup(1M), vgcfgrestore(1M), vgextend(1M), vgreduce(1M), intro(7), lvm(7). vgmove(1M)
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