Use of LVM in Virtualization

[lucho115]

I have used smeserver for 8 years without problems, so now i am trying distros for virtualize mys servers, rigth now i am trying proxmox so i saw if exist eny info about smeserver and yes i found this link en the wiki : http://pve.proxmox.com/wiki/SMEServer_KVM, but the part of this wiki page that most get my atention was this:
"
SMEServer LVM Recovery

SMEServer stores it's data in LVM2. On corruption of the superblock or metadata use a Knoppix LiveCD for recovery and follow instructions at:
SMEServer LVM Recovery using Knoppix LiveCD
Suggestion: Avoid LVM for a VM! To install SMEserver without LVM, use the following command at installation time: "sme nolvm"
"

Its actually true? iam using smeserver for 8 years in many instalation and never have any problem with lvm, but i run allways in baremetal, why in virtualization LVM is not recommended? i dont see this advertation in others distros. Can anybody help me to understand?
thks and sorry about my english

 

[lucho115]

Hi, and now i see this wiki page: http://pve.proxmox.com/wiki/Software_RAID
Where say that proxmox use want to use LVM2 to do snapshots, so ? why LVM is not recommended to virtual manchines and in other hand its useful to do snapshots?
thnks

 

[e100]

I do not use SMEServer, but I have dozens of linux KVM machines that are using LVM.
No issues with corruption, not sure why someone would have suggested to avoid LVM.

 

[webfrank]

Hi, I have a CentOS 6.2 with RT support ticket in it installed with LVM inside proxmox and it suffers of filesystem corruption after proxmox backup (wichi uses LVM snapshots backed by iSCSI). No other VM on same node suffers of corruption, only the one using LVM. No idea why bu I've disabled backup and I'm using bacula to backup RT data.

 

[e100]

I've not seen this, most of my Linux KVM VMs are debian with just a few CentOS.
Are there any kernel messages in the guest when this FS corruption happens?

Here is a great resource for all things LVM related:
http://serverfault.com/questions/279571/lvm-dangers-and-caveats

 

[lucho115]

Thanks for all yours responses but no one told me if its safe to use lvm in virtual manchines. And in other hand if anyone read this link: "http://serverfault.com/questions/279571/lvm-dangers-and-caveats" no one want to use lvm anymore, jeje, i dont know i have no issues with my systems in 10 years od work, the only one that i remember and can be because of lvm was 1 year ago in one installation of ubuntu server 10.04 where i use software raid + lvm2 and the filesystem became corrupted during an mysql update, i cant recover the lvm, in other word i recover but its keep going to corrupt state in hours i dont know why, so thanks to a backup i reinstall all system without lvm and have no ore problems in 1 year. Anyway the answer that i find its about virtualization, can anybody with experience tell me why not to use lvm? and in that case what to use? because there no altenatives i think.
thks and sorry about my englis again.

 

[lucho115]

No responses to my question? So lvm its not safe??? Its shocking for me but seems its knows for many people including the proxmox developer like no one pay attention to this post.
thks.

 

[e100]

No responses to my question? So lvm its not safe??? Its shocking for me but seems its knows for many people including the proxmox developer like no one pay attention to this post.
thks.

I responded previously that I use LVM in many VMs and have never had an issue.
The link to serverfault I provided talks about all the bad things that can go wrong with LVM and how they can be mitigated.

The issue webfrank reported above is concerning. I can only speculate but I doubt that issue is because of just LVM, maybe a saturated network to the iSCSi was partly to blame or maybe the kernel in CentOS 6.2 suffers from some LVM issue.

Every choice you make has a risk, "safe" is for you to decide.

I think it is perfectly safe and for added safety I also maintain multiple backups that are tested regularly.

 

[dietmar]

No responses to my question? So lvm its not safe??? Its shocking for me but seems its knows for many people including the proxmox developer like no one pay attention to this post.

e100 already answered your question.

 

[lucho115]

e100 already answered your question.

dietmar, thks for the response, but e100 didnt answer my quiestion, my really question is why lvm is not recommented and in other hand proxmox prefer use of lvm insted of loop devices to can use snapshots?
thnks

 

[dietmar]

why lvm is not recommented

LVM is recommended - we use it on all installations by default.

 

[half_life]

To clarify maybe, LVM is a good thing to store your virtual machines on. Using lvm inside your virtual machines may have some performance penalties in my opinion but it DOES work. Using LVM to store a virtual machine improves performance.

 

[lucho115]

To clarify maybe, LVM is a good thing to store your virtual machines on. Using lvm inside your virtual machines may have some performance penalties in my opinion but it DOES work. Using LVM to store a virtual machine improves performance.

OK, so put vms in lvm storage is a good idea, but when you expand a lvm that is used like / for the vm1, do you have to do any process in the vm guest? or all in host with the vm1 down? thks

 

[udo]

OK, so put vms in lvm storage is a good idea, but when you expand a lvm that is used like / for the vm1, do you have to do any process in the vm guest? or all in host with the vm1 down? thks

Hi,
if you have an physical machine and you replace the hdd with an bigger one, where you copy before the content from the small hdd, do xou have to do any process to use the additional space?

Yes of course! But why it's should be different with an virtual machine??

If you expand an logical volume from a VM, it's the same as if you build a bigger disk inside...

Udo

 

[half_life]

Back up the VM first. re-size the lvm volume. Expand the VM filesystem using resize2fs within the running VM. Straight forward and easy. Don't skip backing it up first or you may lose data. All of this is assuming a linux VM. It is similar for WinXX machines.