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[Xen-users] LVM or file storage?

  • To: xen-users@xxxxxxxxxxxxxxxxxxx
  • From: Boris Senker <senker@xxxxxxxxx>
  • Date: Sun, 11 Feb 2007 19:27:55 +0100
  • Delivery-date: Sun, 11 Feb 2007 10:33:36 -0800
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  • List-id: Xen user discussion <xen-users.lists.xensource.com>

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?



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

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