Re: [Xen-users] Partition vs disk images

[Rudi Ahlers <Rudi@xxxxxxxxxxx>]

Fajar A. Nugraha wrote:
> Rudi Ahlers wrote:
> > Joseph L. Casale wrote:
> > > > This is for use at home, so in reality it probably doesn't matter 
> > > > -- I just don't want to make any *really* stupid moves.     
> > > I would seriously recommend LVM, its so flexible
> > But is there really a performance difference between LVM & file based 
> > VM's?
> Yes, but depending on how you use it, the effect might not be what you 
> expect.
> Example 1 :
> - you have 16G mem : 4G for domU, 12 G for dom0
> - 1 domU running, with 4G root filesystem
> In this scenario, you'd most likely find file-based VM perform better 
> since dom0 will cache domU's root fs.
> Example 2 :
> - you have 8G mem : 7G for for 7 domUs (1G each), 1G for dom0
> - each domU comes with 4G root filesystem
> In this scenario, the performance of file-based VM will be lower 
> compared to LVM-based VM, due to dom0's filesystem operation overhead 
> (including journaling).
> There are other pros and cons for file vs LVM. Personally, I prefer 
> LVM with each LV on dom0 maps to a partition on domU (hda1,sda1, etc) 
> because :
> - I can easily convert a domU into a physical machine if necessary
> - I can easily mount domU's fs directly on dom0 (e.g for 
> troubleshooting purposes)
> - I can get per-LV I/O statistic from dom0 using tools like iostat
> - I can use LVM snapshot to backup domU's fs without shutting it down
>
> This setup also means that I can't create a VM using frontends like 
> virt-manager (which maps file/LV/partition on dom0 to a disk on domU), 
> but that doesn't matter since I prefer to create VMs manually using 
> prebuilt-template anyway :D
> Regards,
>
> Fajar
ok, what you're saying does make sense, so....


- If you say you can easily convirt a VPS to a physical machine, do you 
just move the LV to a new machine?
- I can mount image based domU as well :)
- But doesn't xen have IO stats as well?
- I prefer not to use snapshot backups, since it makes it more difficult 
to restore just one or two files. We mainly use cPanel & Plesk for our 
hosting, so I use the control panel's backup over FTP instead

--

Kind Regards
Rudi Ahlers
CEO, SoftDux

Web:   http://www.SoftDux.com
Check out my technical blog, http://blog.softdux.com for Linux or other 
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