[ovirt-devel] Re: Image Transfer mechanism queries/API support

On Mon, 27 Aug 2018, 20:10 Suchitra Herwadkar, < Suchitra.Herwadkar(a)veritas.com&gt; wrote: Correct. Here is more detailed description. 1. Find which host can access the disk. Check on which storage domain the disk is located, and to which data center this storage domain belongs. For example, in this setup: dc1 host1 host2 storage1 disk1 dc2 host3 host4 storage2 disk2 If we want to backup/restore disk1 we should run our program on host1 or host2 so you can use unix socket, and avoid sending the data over the network. If you cannot run your transfer program on host1 and host2, you must use HTTPS and send the data over the network. The host performing the upload should also be active. If the host is in maintenance, the disk will not be attached to this host. 2. Balance the backup/restore on all available hosts Check how many transfer are active on all available hosts, and schedule a new transfer on a host which is less busy. For reference, for virt-v2v imports, copying 10s of 100g images from VMWare to RHV, we got best results when running 2-3 imports on 4 hosts, compared with running 10 imports on one host. There is a useful document about virt-v2v performance recommendations crated by our scale team. I think the recommendations should hold for backup/restore. Daniel, can you share a link to the document? 3. Starting the image transfer Once you chose a host, you can start a transfer: - from your management system, and run the transfer program on that host - or run the transfer program on the host, and let it start the transfer virt-v2v took the second approach. This way the transfer program is easy to test, but you may find the first approach better for your needs. To start the transfer on the current host, you can can use the host hardware id. The best example for this virt-v2v rhv-upload-plugin (BSD license): https://github.com/libguestfs/libguestfs/blob/master/v2v/rhv-upload-plugi... 4. Transferring the data First check the host capabilities using OPTIONS request and HTTPS: http://ovirt.github.io/ovirt-imageio/random-io.html#options This will tell if the local imageio daemon supports zero and flush operations, and unix socket. All operations are supported since 4.2.3, but robust program should handle older daemon not supporting the new APIs. If the daemon supports unix socket, and you started the transfer on the same host your transfer program is running, you should close the HTTPS connection, and open a new one using unix socket, to get 15% better performance with less CPU usage. If the daemon supports zero you can use PATCH/zero request. With 4.2.6, this can give significant performance improvement. if the daemon supports flush you can defer flushing, possibly improving performance with some storage. In all cases you should use reuse the same connection for all requests, and always consume the entire response for all requests. The best example for this is imageio examples upload script (GPL license): https://raw.githubusercontent.com/oVirt/ovirt-imageio/master/examples/upload But note that this example works only for local upload, we are working on improving it to support also remote uploads, see here: https://gerrit.ovirt.org/c/93327/ With this patch, if you can use Python, doing: from ovirt_imageio_common import client client.upload(filename, url, use_unix_socket=True) Will do the right thing. If you cannot use Python you can use this as a reference how to implement the same thing in other languages. All this will be eventually documented properly. Nir