Re: [Xen-users] Cheap IOMMU hardware and ECC support importance

[Gordan Bobic <gordan@xxxxxxxxxx>]

On 2014-06-26 17:12, lee wrote:
> Mihail Ivanov <mihail.ivanov93@xxxxxxxxx> writes:
>
> > So next thing I've read about RAID, so I am thinking of raiding 2 x WD
> > Black 2 TB. (Should I do software raid or hardware raid?)
> Software raid can mean quite a slowdown compared to hardware raid.
The only situation where hardware RAID helps is if you have
a _large_ battery backed write cache, and then it only helps
on small bursty writes. A recent x86 CPU can do the RAID
checksumming orders of magnitude faster than most RAID card
ASICs, and hardware RAID cache is completely useless since
anything that is likely to be caught in it will also be in
the OS page cache.

The time where hardware RAID was worthwhile has passed.

> Disks fail.  The only question is when.
All the time. :)

> > Also I will be using ZFS and my Dom0 will be Fedora.
> Fedora for a dom0 is a rather bad choice.  Fedora is an experimental
> testing distribution with a very limited lifetime and prone to
> experience lots of unexpected or undesirable changes.  It is not suited
> for servers, which you can tell by all the things you get installed by
> default and by what they perceive as their user base.  It's targeted 
> for
> laptops, maybe desktops, and the makers of it don't care and don't want
> to hear what its users think.  Unless you have a requirement to use 
> very
> recent software which you cannot have otherwise, or if you want to try
> out new things, it doesn't make sense to use Fedora.
True, and very unfortunate. Doubly so because my preferred distro (EL)
is based on Fedora. The problem is that the quality (or lack thereof)
trickles down, even after a lot of polishing.

> > The question I am still pondering is whether I should get an E3 Xeon
> > (no E3's with IGP are sold in my country), an 6-core E5 Xeon or AMD FX
> > 8***,
> Is power consumption an issue you need to consider?
>
>
> As someone suggested, it might be a good idea to go for certified
> hardware.  My server is going down about every 24 hours with a flood of
> messages in dom0 like "aacraid 0000:04:00.0: swiotlb buffer is full 
> (sz:
> 4096 bytes)", and it's actual server hardware.  I made a bug report a
> while ago; nobody cares and I keep pressing the reset button.  You
> probably don't want to end up like that.
Hardware RAID is just downright evil. I use plain old SATA with
on-board and cheap add-in controllers and find that to be by far
the least problematic combination.

> And after spending quite a bunch of money on hardware, you might want 
> to
> use something else than xen.  Give it a try and set up a couple VMs on 
> a
> testing machine so you get an idea of what you're getting into, and
> reconsider.
Alternatives aren't better, IMO. Having tried Xen, VMware and KVM,
Xen was the only one I managed to (eventually) get working in the
way I originally envisaged.

Gordan

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