Should I use a CoW filesystem on my PC if I only wanted snapshot capabilities ? Post: 303044797

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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

03-04-2020

Registered User

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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vxsplitlines

vxsplitlines(1M)														  vxsplitlines(1M)

NAME

       vxsplitlines - show disks with conflicting configuration copies in a cluster

SYNOPSIS

       vxsplitlines [-g diskgroup] [-c daname]

DESCRIPTION

       If  you	import	portions  of a disk group on different systems, this can lead to conflicting configuration copies on the disks of the disk
       group.

       If the configuration information in a disk group is ambiguous, it may not be possible for Veritas Volume Manager to determine which config-
       uration	copy  is  most up-to-date.  (This is usually termed a serial split brain (SSB) condition when it occurs in a cluster.)	You cannot
       import a disk group in this state unless you specify which disk's configuration copy to use.

       You can use the vxsplitlines command to see which disks in a disk group have conflicting configuration copies,  and  use  this  information
       together with your knowledge of the history of the disk groups' usage to determine which configuration copy is most valid.

       The output from vxsplitlines displays the vxdg commands that you can run to import the disk group using the available configuration copies.
       The -o selectcp option of the vxdg import command is used to select the configuration copy to use for the import.

OPTIONS

       -c daname Display the SSB IDs for each disk that are stored in the configuration copy on the disk specified by its disk access name.

		 Note: Although the SSB IDs for some disks may match, this does not necessarily mean that those disks' configuration  copies  have
		 recorded  all	the configuration changes. When viewed from some other configuration copies, the SSB IDs of the same disks may not
		 match.

       -g diskgroup
		 Specifies the disk group. If a disk group is not specified, the default disk group is used as determined from the  rules  on  the
		 vxdg(1M) manual page.

EXAMPLES

       Display the disks on each side of the split in the disk group newdg:

			vxsplitlines -g newdg

       Display the SSB IDs stored in the configuration copy on disk c2t4d0:

			vxsplitlines -g newdg -c c2t4d0

NOTES

       The vxsplitlines is primarily intended to be used with private disk groups, but it also works with shared disk groups.

       The version number of the disk group must be 110 or greater.

SEE ALSO

       vxdg(1M)

       Veritas Volume Manager Administrator's Guide

VxVM 5.0.31.1							    24 Mar 2008 						  vxsplitlines(1M)