[Xen-users] LVM or file storage?

[Boris Senker <senker@xxxxxxxxx>]

Hi guys,

my apologies for the question probably often asked, but I cannot make 
up my mind and I am kind of new in Xen.
To cut a long story short, I have a Xen 3 installation on the local 
server, with two fully operational CentOS 4 guests. One guest is 
intended for local LAMP + Samba, the other will be local network 
router/firewall/internet gateway with 2 NICs.
Had both setup to mount from file, now created one using LVMs. I had 
problems with dd if-ing a 150 GB samba.img file to be used for Samba 
mount (file too large), so went playing to do the same with LVMs.
Main OS (0) is mounted from /dev/sda (SCSI), the guests are mounted 
off software-raided SATA disks (sdb and sdc) - /dev/md0 (sdb1 + sdc1) 
is a 30 GB partition mounted as /xenstuff (no LVM, used to store 
images and stuff) and /dev/md1 (sdb2 + sdc2) is a LVM partition, used 
to boot guests off.
/dev/md1 is a LVM partition, where for ex. guest1 has a logical group 
guest1, with logical volumes root, swap, tmp, samba.
Recreated with LVM support, all set and mounted using separate 
logical volumes. Working beautifully. So does with image files, though.
I don't have anything on /dev/md1 mounted permanently in domain0, can 
mount it like mount /dev/guest1/root /xendomains/guest1 if needed, 
but what I really liked about using file images for guests is that I 
could easily move them around or have them rsynced (or backed up in 
any way) at a breeze.
What I like about LVM is that I can easily and more efficiently 
manage large partitions, extend them and manipulate them, but I lose 
that simple copy-the-image-files convenience.
Load wise, loop doesn't make loads anymore (since not used with LVM; 
this box has an old Pentium IV 2.8 GHz CPU without HT so loop loads 
are kind of noticeable at times) and I *think* the CPU usage is hence 
lower (haven't tested performance yet, but I think LVM storage is 
faster for Samba operations - opening a folder full of images in 
thumbnail view from Windows box seems faster than with file image mounts).
Honestly, I can't decide whether to incline to file images (visible 
as stored files, can copy/move around easier, the location where 
images are stored is mounted hence accessible in a simpler way, had 
above mentioned problems with images too big like samba one), or LVM 
(seems more flexible for resizing, large partitions OK, can't have 
their container location mounted permanently, can't simply move 
around/backup images, loop doesn't load, not sure how to backup those 
yet - from what I see, LVM snapshots are still not too stable? In any 
case, burning the file image to DVD and/or transporting it anywhere 
seems simpler than whatever used for LVM).
Any advice pro/against any of storage options - file or LVM?

Thanks,

Boris

PS. I am really having fun with Xen, really fascinating :)


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