David Bell wrote:
> Imran Chaudhry wrote:
>> Hey all, I'm embarking on a project involving virtualization and
>> thought I'd consult the list in a wisdom-of-crowds fashion :-)
...
That's a good comprehensive summary by David. I'll only add our
experience FWIW...
We've opted for free/GPL where possible for our virtualisation. We're
using Xen as provided by Debian (an old version I have to admit). It
has served us well for several years.
We're using an HP DL380 with redundant PSUs and a SAS RAID and a remote
(web) management card. It all works with Debian including the
management card's serial console access to the server. For even higher
availability you can mirror DIMM pairs, or have one DIMM pair as a
spare, or just use the whole lot. I've had better experience with HP
hardware and Linux than Dell hardware. HP even supports Debian
(installation) on certain server hardware, and they use it internally I
believe. They're my first port of call for new server hardware now.
The RAID has a battery backed cache - a must for reliable operation.
Also ensure you use a decent UPS and have the server shutdown on a low
battery condition. This is easy with a APC SmartUPS with an ethernet
management card.
We run 11 (DomU) servers on the DL380 such as mail, samba, proxy,
database and our own server apps. We backup the DomUs to another box
which is ready to run any of the backup DomUs with a single command.
Our biggest bottleneck has been storage I/O. The CPUs are barely
touched in comparison when averaged over 24 hours. I could improve
write performance by moving from RAID6 to RAID10 but we need the storage
space. I could also upgrade to 15K SAS disks, but again we need the
space and you can buy bigger and cheaper 10K SAS drives. Much I/O
performance is gained by enabling the RAID card's _write_ cache - but
you must have a battery backed cache for this, otherwise you risk losing
data and breaking your filesystem _and_ journal.
I'm starting to take a more serious look at KVM. It's proving a real
boon on my desktop PC when I need access to a Windows install. I think
KVM will be your ultimate solution, as it will be for us, although we're
sticking firmly with Xen for now, especially for Linux VMs anyway.
I believe the creators of KVM have a product to help manage VMs but I
believe it's orientated towards Windows XP desktops. There must be GPL
graphical tools to help with KVM and Xen by now. It's worth a look
around. As for Xen, the commercial offering has a management GUI. I'm
afraid I've never really spent much time looking for management GUIs so
I can't help you there.
Your Dell is fine for most virtualisation purposes but if you do buy
hardware ensure the processor has virtualisation extensions - hard not
to with servers, but do check. Buy as much RAM as you can afford - you
don't want 1 VM to start swapping and affect your other VMs (Done
that!). This is where KVM and Xen differ. You allocate fixed amounts
of memory to Xen VMs (DomUs) where as KVM shares one big pool of memory,
with the VMs being processes (Others on the list will be able to explain
the difference with more clarity/accuracy!).
Storage is easier to upgrade later should you need more. We've opted to
use low latency SAS disks in a RAID for VMs and backup to cheaper slower
SATA disks.
Simon C.
