Re: Download RHEL4

General Schvantzkopf wrote:
On Mon, 20 Oct 2008 09:20:53 -0700, Kenneth Brun Nielsen wrote:

On Oct 17, 7:20 pm, General Schvantzkopf <schvantzk...@xxxxxxxxx> wrote:
On Fri, 17 Oct 2008 06:03:40 -0700, Kenneth Brun Nielsen wrote:

RHEL requires a subscription however there are free clones available
which are built from Redhat's source RPMs. The main clones are CentOS
and Scientific Linux.
Are they similar (from any application's point of view)? Let me point
of, that I'm not in a "trial-and-error" business. I can't afford to make
an error due to some strange divergences between the guaranteed OS
(RHEL4) and any ALMOST similar OS, ultimately ending up in differerent
results.

Best regards,
Kenneth

The Clones are exactly the same in terms of executable code. The place where they differ is in identification strings so if an application checks to see if it's RHEL 5 it might print out a warning if it sees that it's CentOS 5 but it will almost always run.

No, they're not. Please don't spread this misinformation. CentOS 4, for example, uses Yum, which finds the nearest repository from around the world, rather than up2date, which is a nightmare to maintain and has a much more awkward backend. It also has an 'extras' repository that contains a good, working copy of 'mock' for building software packages in a well-defined environment, and NTFS kernel modules.

RHEL 5, for example, also does this amazingly stupid split-up of its components into 'Server', 'Supplementary', 'Productivity', etc. The CentOS breakdown is rather different and based on licensing and whether it's in the RHEL source tree, such as 'centosplus'

The differences are normally very modest. CentOS add-on components normally behave extremely well with RHEL, and I've even written tools to turn a CentOS machine to RHEL, and vice versa.


For Virtualization I use VMware Server, both 1.0.7 and 2.0. Server is free. 1.x only supports 4G VMs, 2.0 increased the memory limit to 8G. The performance limitation of VMware Server is in IO. If you want the VM to be able to access host directories you have to do it through NFS or SAMBA. If you are running entirely on a Virtual disk rather than accessing a host directory the performance is at least 90% of native. If you aren't IO bound then Server is a great solution. If you are IO bound you would want to consider one of there paid for products. I've only tried Workstation which looks exactly like Server except that it has the capability of mapping a host directory into the VM. Mapped directories fix the IO performance problem, it's almost the same performance as native.

I haven't tried VirtualBox lately. The last time I looked, VirtualBox was limited to 2G of memory per VM which is useless for my purposes. That was a while ago, they may have fixed that by now. VirtualBox has the directory mapping feature included in the free version.

The other alternative is KVM. Redhat just bought Qumranet which is the company behind KVM. KVM is very promising, but it's not ready for real work yet. When I looked at it last spring the performance of VMs that did no IO that was external to the VM was better than VMware, it was around 95% of native. However the virtual IO performance was horrendous, I found that my Verilog simulations took four times as long, as they did on VMware Server, if I was running on an NFS mounted directory. When I queried their forums they claimed that there was a way to fix the performance problem, however it was sufficiently complicated at the time that I didn't think it was worth my time. The control GUI on Fedora 9 also wasn't very usable, the GUI for VMware Server 1 is great, 2 switched to a browser based UI which is slower that the old GUI but it's still very usable. My guess is that KVM will be much closer to usable in Fedora 10, but VMware will still be the VM of choice. Also you can run VMware on a CentOS or RHEL host, you won't be able to run KVM on RHEL until RHEL 6.

Xen works just fine on RHEL and CentOS, and has for years. I find that VMware's command line tools bite goat rocks: the concept that you should be running a Windows box to manage a server, or even an X session, seems welded to their brainstems, and it's just not necessary.

Xen doesn't have this problem, although their GUI's could use some maturation and a careful reading of Eric Raymond's famous rant about CUPS and open source interfaces.
.

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