Hello! I had a hobby project where I needed to manipulate xen disk images on remote systems, that used a model similar to libirt's remote support. Based on what I learnt from it, I came up with a possible model for libvirt's remote storage support. I present it here for discussion. We typically store the images in volumes on LVM, or in dedicated file system folders. The folders and volume groups usable by libvirt can be limited in a config file. It is probably not neccessary to differentiate between defined and created files, as you can not stop and start a file like a domain, you either have it on disk, or not. Libvirt should not store information on these files, everything should be checked/listed on the fly, so that if you just copy an image to a directory, libvirt can deduct all information (well, all it can) on it, and handle it just as if the file was created by it. The handle for the file is its path, plus its virConnect object (i.e. the host it is on). For consistency, it may be possible to create an object for it, but as disk images have no persistent properties apart from what is on the disk, and it can always be checked from there, it provides no extra functionality. I think there is no need to support remote files explicitly, as the domains mount local files/volumes. The file/volume may actually be mounted from a NAS or SAN, of course, but it does not matter because we use the local path names, and AFAIK all virtualization tools use local files or local devices as blockdevs. I have added compression to the mix because it is immensely useful. I have used lzop in my project, and a full backup and restore was much faster when using a compressed backup file, than with and uncrompessed one. It conserves disk space, as well as cpu/bus capacity. Zeroing out newly allocated files, helps with compressed backups, as well as security. It also means that no holey files can be used. The objects we are dealing with are disk images. They have the following properties: -Path: The unix path of the file ( /mnt/images/fc7.img or /dev/VG/fc7) -Compression: Mountable/compressed -Type: Plain file/LVM volume/ What else? -Size -Filesystem: swap/ext3/xfs/.... -Is it mounted? We can do the following operations on the images: Create -connection -filepath -size Allocates a new image of the given type, size, and name. Libvirt should parse the filepath, and determine the base path, check if it's a directory or a VG, check if libvirt is allowed to operate on the path/VG, then create the file/volume. For security reasons zeroing out the allocated space should be a non-optional step of the allocation. DirectoryList -connection -directorypath Plain ls functionality, that returns the list of files, and any subdirectories. If called on a VG, it returns the volumes in it. Info -connection -filepath Returns information on the given file/volume, including size, type, filesystem (if available), whether it is a snapshot (if a volume), and whether it is mounted or not. size can be determined by ls or lvinfo, filesystem by 'file' command. Delete -connection -filepath Delete the file/volume. Find out if it's a file or volume, and rm or lvremove it. Grow -connection -path -filename -newsize Grows the specified image to the given size. The newly added space is zeroed out. Shrink? -connection -path -filename -newsize Shrinks the specified image the the given size. It's very tricky, because to avoid data loss, we need to analyze the file system size. Of course, we can just say that it's the reponsibility of the user, after all, we allow him to outright delete the file as well. We may combine it with Grow, and call it Resize. Growfs -connection -path -filename -newsize? Grows the filesystem on the image to fill the size of the image, or the given newsize. Can only be used on umounted images. It is neccesary because some filesystems may not be grown while mounted, so the guest can not do it on its own. Shrinkfs -connection -path -filname -newsize Shrinks the filesystem to the given size. Same coniderations apply as with growfs, may be combined to Resizefs? Snapshot -connection -filepath -filesize Creates a snapshot of the given image. It is only possible with images on LVM. Should return the snapshot image name. The snapshot can later be deleted with Delete. CopyTo -connection -source filepath -target connection -target filepath -snapshot flag -archive flag -overwrite flag Copy the source image to the target image. If connection is on another machine, then it's a network copy. If the snapshot flag is true, then first create a snapshot of the source image, copy that, then delete the snapshot. If the archive flag is active, then the target file will be archive file (compressed). If the overwite flag is active, then the target file is overwitten, if it exists. Otherwise existing files are not changed. Even if the source file is compressed, the target file is uncompressed, unless the archive flag is set. CopyContents -connection -source filepath -target connection -target filepath -snapshot flag Copies the contents of the source file to the target file. The target file must already exist, and be no smaller than the source file. The contents of the target file are overwitten, and any extra space is zeroed out. Archive -connection -filepath compresses the given file. Makes sense only on files, not volumes. Unarchive -connection -filepath uncompresses the given file. Makes sense only on archved(compressed) files. StorageInfo - connection Returns information on the node's storage configuration. What kind of filesystems it can handle, What are the accessible file / VG paths, what's the free space on them, etc. A typical usage scenario could be something like this: Aconn=getVirconn("ssh:Ahost"); //Open the connection to host A Bconn=getVirconn("ssh:Bhost"); //Host B will hold our backup image Ainfo=StorageInfo(Aconn); //Get Ainfo AVGPath = <get the first usable VG path from VG info> Newimage = Create(Aconn, concat("AVGPath", "newimage", 100000); //A 100Mb volume is created and zeroed out. CopyContents(Aconn, NewImage, Aconn, "/images/ghost/FC7default.img", no); //Copy our pre-created FC7 image to the new image Growfs(Aconn, NewImage, 0); //Grow the copied filesystem to fill the whole volume. <Here we define a new domain, and use NewImage as the name of the backing image for the guest's block device> <Start the new domain> Copy(Aconn, NewImage, Bconn, "/mnt/backups/backup23image", snapshot=yes, archive=yes, overwrite=no); //Make an LVM snapshot of NewImage, and copy it to Host B on the given filename, compressing it on the fly, then remove the snapshot <Stop the domain> CopyContents(Bconn, "/mnt/backups/backup23image", Aconn, NewImage, snapshot=no); //Restore the backed-up image to NewImage, decompress it on the fly. <Start the domain> <Stop the domain> Grow(Aconn, NewImage, 200000); //Grow the volume to 200MBs Growfs(Aconn, NewImage); //Grow the fs on the volume to fill the volume <Start the domain> ..... Best regards István