The officially official Devuan Forum!

Micronaut

Member

Registered: 2019-07-04

Posts: 236  

LVM -- useful or not?

So far I have always avoided using LVM as it seemed like an extra layer of abstraction, and to my mind code, on top of any other drivers needed to access the drives. Does LVM really add any overhead to disk access? Can it slow down a system at all? Or is it only relevant at the install phase, and then at the time of any modifications of the disk layout?

ralph.ronnquist

Administrator

From: Battery Point, Tasmania, AUS

Registered: 2016-11-30

Posts: 1,411  

Re: LVM -- useful or not?

yes it adds overhead; every block access needs to go through the mapping tables.

rolfie

Member

Registered: 2017-11-25

Posts: 1,263  

Re: LVM -- useful or not?

Since many many years I am using LVM in combination with luks encryption. One PW for decryption for several LVM volumes.

Yes, its overhead, but you do not see or feel a major delay on modern computers.

ralph.ronnquist

Administrator

From: Battery Point, Tasmania, AUS

Registered: 2016-11-30

Posts: 1,411  

Re: LVM -- useful or not?

Hopefully I can say this without pushing anyone into defensive mode: my personal opinion is that LVM a total waste of energy. I.e. actual energy wasted by extra processing, turning into heat and whatnot for no practical gain. Just because it's possible. But yes, there is that fascinating idea of theoretical flexibility, which basically noone uses.

fsmithred

Administrator

Registered: 2016-11-25

Posts: 2,651  

Re: LVM -- useful or not?

Wasted energy, maybe, but where else can you experience the thrill (terror) of resizing a partition while it's mounted and in use?

Micronaut

Member

Registered: 2019-07-04

Posts: 236  

Re: LVM -- useful or not?

Yeah, I had the impression from the way it was pushed in the installer that it was a 'normal' thing, but I guess LVM is not very widely used? I always opted not to use it because I realized that 'dynamic' resizing could only be possible by fragmenting the actual allocation of the partitions, with possibly major performance implications.

I guess what made me think about it again was preparing to use SSDs. Fragmentation of partitions would not be a performance issue on SSDs. But I've never had an SSD in any system yet. They always seemed too expensive, and somewhat unreliable. I keep hearing they fail little or no warning. Unlike spinning disks that usually give you SMART warnings for a while before actually becoming unusable. But the durability and reliability of SSDs has been increasing, and the speed advantages are tempting for uses like gaming.

It sounds like I still don't need to use LVM. Just plan my partitions well so I don't have to re-map them later.

delgado

Member

Registered: 2022-07-14

Posts: 247  

Re: LVM -- useful or not?

I like to know where files physically exist** and the concept of 'partitions with file systems'. Things like LVM or btrfs/zfs (with sub-volumes) are too complicated for me.

.
** About 15 years ago, a (cheap) power supply died and took two HDDs with it. The HDDs could be repaired, but the journey was really unpleasent.
1st solution without soldering: Buy an identical HDD and use the controller board to access the files.
2nd solution with soldering: Replace the protection diodes on the controller board and the HDDs are as good as new.