Re: [tlug] server partitions, LVM, and Xen

[Edward Middleton <emiddleton@example.com>]

Keith Bawden wrote:
> You could also use have your Virtual Block Device  based on a normal
> physical partition.

You could but then you couldn't resize it or easily remove it.

> Then again I wonder what type of performance hit you would see when
> using a file as Curt suggested.

In terms of speed you probably won't notice it but you will use more
system resources.  The host filesystem is going to cache the device file
then the xen filesystem is going to cache files on the xen filesystem.

> Also, I wonder if a file based
> approach would help simplify things when migrating instances to new
> servers.

Not much[1],

1. copying logical volume

a. create the remote logical volume of the same size

# xen_len=`lvs --noheading -o lv_name,lv_size | \
  grep xen|sed -e 's/[ ]*xen[ ]*//'`
# ssh me@example.com "lvcreate -L$xen_len -nxen /dev/vg"

b. copy image
# dd if=/dev/vg/xen | ssh me@example.com "dd of=/dev/vg/xen"


2. copy image file

# scp /home/me/xen me@example.com:/home/me/xen

The main advantage of using a file is that it allows you to use a sparse
partition. i.e. you won't have to allocate the space until you create
files on the filesystem.

Edward


1. I presume by migration you mean copying the system image.  Live
migration isn't going to be effected by they choice of file or block device.