Pre-kernel: Perhaps you could do gPXE -> read-only iSCSI SAN -> MBR -> NTFS Partition -> NTLDR -> specially-crafted NTBOOTDD.SYS (for VHDs) -> "Master" VHD
Post-kernel: MS iSCSI Initiator and Michael Brown's 'sanbootconf' driver re-establish the SAN. WinVBlock creates a new "child" VHD on a partition on the local HDD, with the "parent" VHD still the same one on the same iSCSI SAN. Does this seem like it'd satisfy your goals? Do you need anything to persist beyond a reboot? What is the OS you are hoping to boot on the clients? If gPXE development isn't really involved, perhaps I could request private correspondence for any WinVBlock-related matters, if you please? If tweaks need to be made to gPXE, then by all means, I would agree that this forum would be appropriate. :-) Thanks again for your interest! - Shao Miller ________________________________ From: Kenton Varda [mailto:tempo...@gmail.com] Sent: Wednesday, May 04, 2011 11:21 To: Miller, Shao Cc: gpxe-devel@etherboot.org Subject: Re: COW Overlay in WinVBlock -- willing to implement I'm aware that I can set up COW on the server side, but I'd really rather that writes didn't cross the network at all. It's not uncommon for guests to want to install additional games which can be as much as 10GB each, and my machines have 60GB local SSDs which I'd like to utilize. In fact, longer-term it would be nice to use those SSDs as read caches in addition to write caches, maybe even sniffing blocks being sent to other machines on the network and precaching them. Typically, everyone loads the same game at the same time, and games need to load a lot of data, so it would be neat to avoid transferring that data over the network 12 times. That said, this doesn't appear to be a significant performance problem in my existing setup, so it is not a priority. (Actually, I have already written code that implements this idea as a userspace daemon on top of NBD, though it seems to have some bugs still.) I'm also aware that commercial solutions exist, but I'd rather use an open source solution that I can customize, e.g. with the features I mentioned above. Also, the commercial solutions I've found require running a Windows server, which I'd like to avoid. And anyway, implementing this would be fun. :) -Kenton On Wed, May 4, 2011 at 5:27 AM, Miller, Shao <shao.mil...@yrdsb.edu.on.ca> wrote: Good day, Kenton. I'm currently working on some serialization/deserialization code in order to simplify developing support for Microsoft's [acquired] VHD disk image format. Once implemented, the "differencing" feature of VHD image files will provide copy-on-write functionality. For example, I'd like to be able to boot from a master VHD pre-kernel, then have WinVBlock continue with a delta. However! Since you've e-mailed the gPXE developers' list, I suspect that you are more interested in SAN CoW of some sort. This is currently possible using Linux' device-mapper, and serving the CoW devices. Did you see this article?: http://etherboot.org/wiki/appnotes/cow CoW-capable SAN target software seems to be a popular wish. A fellow recently shared a fun video of Ardence: http://www.youtube.com/watch?v=moIuHqIc-PQ&feature=player_embedded I'm not 100% sure how you might be thinking of using gPXE + WinVBlock, or if you would even need WinVBlock. Would you care to share a few more details about the scenario you have envisioned? Thank you for your offer to help with development. When WinVBlock was originally derived from V.'s WinAoE work, it was quite a learning curve, having dwelled in user-land, myself. But before suggesting anything to jump into, perhaps a little more discussion regarding your scenario would be better. Thanks! - Shao Miller ________________________________ From: Kenton Varda [mailto:tempo...@gmail.com] Sent: Wednesday, May 04, 2011 01:35 To: Miller, Shao; gpxe-devel@etherboot.org Subject: COW Overlay in WinVBlock -- willing to implement Hi Shao and gpxe-devel, In a post on this page you mentioned that you are planning to add COW overlay support to WinVBlock: http://reboot.pro/8168/page__st__300 I have a need for this (in order to netboot multiple machines off a common base image), and have not been able to find any existing non-proprietary solution. Can I help you implement it? If so, can you give me pointers on where to start and what to do? I am fluent in userland C (including low-level Win32 and POSIX), but have never ventured into kernel drivers before. FWIW I'm a Google employee, but this is for a personal project. Namely, my house, which is optimized for LAN parties. I currently have 12 machines netbooting Ubuntu over nbd and running games under WINE, but sadly there are a few too many games that don't work. :/ Thanks, -Kenton
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