[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Solution for problems with HyperSCSI and vbds ?
> Thinking about just 3 DOM0 HyperSCSI clients connecting > to the HyperSCSI-Server directly feels somehow more comfortable. > (e.g. a lot easier administration, less points of failiure.) > The 3 DOM0s in this example can then export the HyperSCSI > device(s) via whatever means to the domains > 0. Of course, the absolutely proper solution is to put HyperSCSI into Xen, so that Xen's block device interface could be used by guest OSes to talk directly with the remote disk. However, I wouldn't want to contemplate putting a big gob of code like HyperSCSI into Xen until we have implemented the plan for ring-1 loadable modules support. This would then give us a shared-memory block device interface between guestOSes and the HyperSCSI driver (also running in ring1). The HyperSCSI driver would then talk to the network interface, again using shared-memory. > Thanks a lot for pointing me to this solution ! > I will look into it during the next days (especially performance ;-). I'm looking forward to hearing how you get on. > A propos: > Did you ever make benchmarks about the average or maximum > throughput of your VFR implementation in XEN ? The throughput between domains and the real network interface is _very_ good, easily able to saturate a 1Gb/s NIC, probably good for rather more. However, I'm afraid to say that we recently discovered that our inter domain performance is pretty abysmal -- worse than our performance over the real network, which is simultaneously amusing and sad. The problem is that we currently don't get the asynchronous `pipelining' when doing inter-domain networking that gives good performance when going to an external interface: since the communication is currently synchronous we don't get back pressure to allow a queue to build up as would happen with a real NIC. The net result is that we end up bouncing in and out of xen several times for each packet. I volunteered to fix this, but I'm afraid I haven't had time as yet. I'm confident we should end up with really good inter domain networking performance, using pipelining and page flipping. > Also, did you make some benchmarks about the amount > of performance degradation by using vbds/vds for disk access > compared with using the block device directly (test in DOM0)? Performance of vbds and raw partitions should be identical. Disks are slow -- you have to really work at it to cock the performance up ;-) > Could mounting /dev/sda via enbd be more performant or > at least nearly equally performant to using vds and vbds > because of the additional overhead of vd/vbd use... ?? Performance using enbd should be pretty good once we've sorted out inter domain networking. Ian ------------------------------------------------------- This SF.net email is sponsored by: SF.net Giveback Program. SourceForge.net hosts over 70,000 Open Source Projects. See the people who have HELPED US provide better services: Click here: http://sourceforge.net/supporters.php _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/xen-devel
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