[linux-lvm] creating pv's on LVM's for virtual guests

[Steve Shorter]

On Mon, May 09, 2011 at 03:40:08PM -0600, allan wrote:
> Hi Steve,
>
> I've had mixed results doing that very thing. Two servers perform very differently.
> One mach, an HP DL380G6 w/ dual quad core Zeon and 6 146G disks installed 
> with CentOS 5.5 stock xen, lvm, etc. performs very well. Another machine 
> intended as a low class server, a desktop quad core AMD, 4 SATA disks 
> installed with stock CentOS 5.5 same as first mach, has issues with disk 
> perfomance on every DomU - writes are 1/10 the rate of Dom0 -- I'm still 
> troubleshooting it.
> I see no problem with using LVM on Dom0, carving it up and offering to 
> DomU virtuals and the virtuals using LVM for storage. One thing to avoid: 
> do not duplicate an LVM names within the entire machine. i.e. installer, 
> when told to use LVM, will create a vg of a specific name. If this name 
> is not overridden, and you create multiple DomUs with same process the VG 
> name will be duplicated (as well as the LV names). Avoid name 
> duplication.
> I hope this helps.
>
> Allan


	This is what I do on the host


lvcreate --name ${DOMAIN} --size ${VSIZE}G ${HOST} || exit 2

pvcreate -y -ff /dev/${HOST}/${DOMAIN} || exit 3

vgcreate -y -ff -s32m ${DOMAIN} /dev/${HOST}/${DOMAIN} || exit 4

lvcreate --name data --size ${DISKSIZE} ${DOMAIN} || exit 5

lvcreate --name swap -l 100%FREE ${DOMAIN} || exit 6

mkfs.ext3 /dev/${DOMAIN}/data || exit 7

mkswap /dev/${DOMAIN}/swap || exit 8

	I pass /dev/${HOST}/${DOMAIN} to the quest, and it sees 
a VG ${DOMAIN} with LV's named "data" and "swap" and they are
immediately usable as swap/ext3

	Seems to work. Haven't tested for performance. Your performance issue
above seems to be hardware related??

	Any concerns?


	-steve


>
> Steve Shorter wrote:
>> Howdy!
>>
>> 	I am setting up virtual guests to have a LVM created
>> from the host. It would be good to use LVM's in the
>> guest also.. for easy volume expansion etc...
>>
>> ie. I am creating pv's/vg's/lvms on top of LVM's. It *seems* to
>> work but some of the userland tools need the option -ff
>>
>> 	Does anybody see any issues doing this?
>>
>> 	thanx - steve
>>
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>>
>
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