Gionatan Danti schreef op 07-02-2018 19:42:
I am both a LVM/ThinLVM and ZFS heavy user, so I hope to be impartial
here...
LVM and its lvmthin counterpart are *rock solid* in my experience,
except in the (very) edge case of full thin pool (this was lengthly
discussed in the past, and both Zednek and Jonathan gave accurate
suggestions on how to avoid that).
However, in my experience, the only distribution which keep updated
version of lvm kernel and user space utilities is RHEL/CentOS. I found
Debian and Ubuntu based distributions particularly *bad* at managing
LVM and device mapper targets in general.
This is the reason for the problems but LVM released bad products all
the same with the solution being to not use them for very long, or
rather, to upgrade.
Yes Ubuntu runs a long time behind and Debian also.
As a user, I can't help that, upgrading LVM just like that to have less
"there is a pit here but we won't tell you about that" simply seems also
fraught with peril.
For example, upgrading LVM slightly to 160 caused udev problems I didn't
have before.
So you can blame the distributions, you can also blame features being
released first and proper protection only being added much later.
So if you're on Xenial, you are stuck with the features but without the
protection.
In particular there is a quagmire of situations you can end up with wrt
the shielding and dual activation of the same vg, many times of which
you can only get out of the situation with dmsetup remove, but I didn't
know this at first.
Or you end up in the situation where a PV is missing and you cannot edit
the VG, but in order to remove the PV you have to edit the VG.
A missing cache device cannot be removed without the missing cache
device being present.
I meant to say, you can have 2 disks out of sync and resolving it is not
possible other than by editing config on disk and doing vgcfgrestore.
But you can't do vgcfgrestore without removing a missing PV first.
There is a huge amount of chicken and egg problems because physically a
VG sits inside a PV but logically a PV sits inside a VG and this
constantly causes issues.
LVM just has conceptual problems.
That said, ZFS really is outstanding (especially checksum and
compression, albeit is sorely lacks reflinks). I really have high
hopes for stratis (https://github.com/stratis-storage), which plan to
provide ZFS-like feature using stacked device mapper targets (which
our beloved LVM targets on top).
I cannot write more yet because I don't have ZFS setup yet.
I don't like ZFS too much because it's opaque and Linux support seems to
be flimsy (for example boot support) and the only good documentation is
Oracle but it often does not apply.
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