Re: [Xen-users] Partition vs disk images

["Fajar A. Nugraha" <fajar@xxxxxxxxx>]

Rudi Ahlers wrote:
> Fajar A. Nugraha wrote:
> > 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
> 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?
Depends. The power of this method became apparent when each domU has its 
own VG located on a SAN (or iscsi). I can simply reassign that VG's 
disks to a new machine, and setup the appropriate fstab/grub.conf/initrd 
(I'm only talking about PV linux here). Note that installing to a 
partition (each domU on different disk) has this benefit as well, but 
LVM is easier to manage when you need to resize.
> - I can mount image based domU as well :)
Yes you can :)
This part is actually more of assign-to-domU-disk vs 
assign-to-domU-partition rather than file-based vs LVM-based. If an 
LV/file is assigned to domU disk, you need extra steps (usually 
involving kpartx and/or vgscan) to mount domU's fs.
> - But doesn't xen have IO stats as well?
Yes, but AFAIK it shows only total number of requests.
iostat can show each LVs IO rates (per second) in sectors or in requests.
/proc/diskstats can show each LVs total IO stats.

> - 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
You don't need snapshot backups then.

Regards,

Fajar

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