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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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voldiskadd(8)						      System Manager's Manual						     voldiskadd(8)

NAME
voldiskadd - Adds one or more disks for use with the Logical Storage Manager SYNOPSIS
/usr/sbin/voldiskadd disk-address-list DESCRIPTION
The voldiskadd utility sets up new disks that are added to the system after the initial system installation and configures the disks for use by the Logical Storage Manager. A valid disk label must exist on the disk before using the voldiskadd utility. One or more disks may be specified using a disk-address-list. Disk addresses in the list have the form dskn (for the entire disk) or dsknp (for a specific partition). When specifying multiple disks, use a space between entries. Disk address names relate directly to device names in the /dev/disk directory. For example, here are some valid voldiskadd disk-address-list specifications: # voldiskadd dsk1 # voldiskadd dsk2 dsk3a The file, /etc/vol/disks.exclude, may be used to exclude disks from use by voldiskadd. Each line of the file specifies the name of a disk to exclude (for example, dsk5). The voldiskadd utility prompts the user for a disk group name and disk media name for the disks. If a new disk group name is specified, that disk group is created for the new disks. If no disk group name is specified, the disks are left as unassigned replacement disks for future use. If an existing disk group name is specified, the user is prompted for whether the disks should be designated as spares for the disk group. If a disk is found to already contain non-Logical Storage Manager partitioning, the user is asked whether the disk should be encapsulated. Encapsulation turns each partition of the disk into a volume. A disk should be encapsulated if it contains file systems or data that should not be overwritten. If encapsulation is not desired for a disk, the disk can be initialized as a new disk for use by the Logical Storage Manager. For new disks, all space on the disk becomes free space in the disk's disk group. Context-sensitive help is available at every prompt by typing ?. Also, a list option can be used to get information on available target disks for an operation. The voldiskadd utility supports the following general classes of actions: Initializing a disk with reserved regions and partitions. Disk initialization is performed by calling voldisksetup command. Adding a disk to an existing disk group. This operation can be performed independently of the initialization of the disk drive to add a disk's storage space to a disk group's free space pool. The volassist command may subsequently allocate from that free space. The disk can also be added as a hot spare device. Creating new disk groups in which to import new disks. If no disk group exists for importing disks, the option of creating the disk group is offered. Encapsulating disks that have exist- ing contents. This is the default action for disks that do not have a valid, existing Logical Storage Manager private region, but that do have a disk label. Encapsulation is performed by calling volencap. Reconnecting a drive that was temporarily inaccessible. This situation is detected automatically, by noting that the specified drive has a disk ID that matches a disk media record with no currently associated physical disk. After reconnection, any stale plexes referring the disk are reattached, and any stopped volumes referring the disk are restarted. This reattach action is performed by calling the volrecover script. ERRORS
You may receive the following messages when using the voldiskadd command: Initialization of disk device special-device failed. Error: special-device or an overlapping partition is open. This message indicates that the partition you specified or an overlapping partition on the disk is actively in use. The partition could be a mounted UFS or AdvFS filesystem, initialized as an LSM disk or used as a swap device. special-device is marked in use for fstype in the disklabel. If you continue with the operation you can possibly destroy existing data. Would you like to continue?? [y,n,q,?] (default: n) This message indicates that the fstype of a partition or an overlapping partition is set in the disk label. The voldiskadd command prints this message to warn that a disk partition may have valid data which could be destroyed. If you are sure that the disk partition does not have valid data and that the partition can be added to LSM, you can ignore the warning message by entering y at the prompt. The voldiskadd command will proceed to initialize the disk partition and add it to LSM. FILES
A list of disks to exclude from use by voldiskadd. SEE ALSO
disklabel(8), volassist(8), voldisk(8), voldiskadm(8), voldisksetup(8), voldg(8), volintro(8) voldiskadd(8)
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