Re: [Xen-users] How many guests

[Jonathan Tripathy <jonnyt@xxxxxxxxxxx>]

Hi Michael,

You state that iSCSI is reliable but expensive. But isn't iSCSI nearly free?

I agree with you that Fibre Channel systems are very expensive

Would iSCSI over IP be ok?

Thanks


On 07/06/10 08:12, Michael Schmidt wrote:
> This is not completely correct.
> With a raid 1, you have the read performance of 2 disks and just the 
> write performance of a single disk.
> To the other thinks following this thread:
> If you use a network storage, you have a bandwidth limit with the 
> connection. But in the most cases, the raw bandwidth is not the 
> bottleneck (instead of the IOs per second).
> Network Storages using NFS or NBD are not stable enough in my eyes.
> iSCSI and FC SANs but really stable and expansive as well. But there 
> is another much less expensive way:
> You get the most servers with an external SAS port. There you can 
> connect over a SAS link a JBOD with 12 - 16 disk bays (DAS).
> This disks can be managed by the servers raid controller.
>
> Best Regards
>
> Michael Schmidt
>
>
> Am 06.06.10 23:21, schrieb Bart Coninckx:
> > RAID1 does not perform better than a single disk. It will still 
> > depend on what
> > those 5 to 10 VMs would do. It still might be stretching it. For 10 
> > webservers
> > visited by 5 users per hour: I would say no problem. For 5 heavily used
> > database servers it will be another story.
> >
> > I guess the only real way to find out is to put your guests on there 
> > and try.
> > If you clone them, you will know quite fast.
> >
> >
> > On Sunday 06 June 2010 21:38:54 Jonathan Tripathy wrote:
> > > Thanks Micael,
> > >
> > > I understand what you are saying.
> > >
> > > With a small setup such as a RAID1 array, how many VMs could I rent 
> > > out?
> > > It doesn't matter if it's a small number, it's just to utilise the
> > > server a bit.
> > >
> > > Think it would cope with 5-10?
> > >
> > > Thanks
> > >
> > > Jonathan
> > >
> > > On 06/06/10 20:18, Michael Schmidt wrote:
> > > > Hi Jonathan,
> > > >
> > > > if you plan to migrate existing physical machines to xen VMs, or you
> > > > have some different machines for a comparison,
> > > > you can easy get runtime statistics and calculate the usage. Look at
> > > > the running iostats and cpu usage.
> > > >
> > > > If you plan to rent generic VMs on this server to customers, you disk
> > > > / raid setup will be absolutely the bottleneck.
> > > > A solution at this point is not easy. If you have much write IOs, use
> > > > raid 10 with 4 to 8 disks. With many reads - raid 6 or 50 with the
> > > > same amount of disks.
> > > > In each case i can suggest you 15k rpm SAS disks.
> > > >
> > > > Then you can run 29 VMs. Or 60 VMs with 16GB memory and 2 CPUs.
> > > >
> > > > But note: You cannot set disk priority to the VMs. So if one VM does
> > > > heavy disk IO, all off the other VMs slowed down.
> > > >
> > > > Best Regards
> > > >
> > > > Michael Schmidt
> > > >
> > > > Am 06.06.10 20:45, schrieb Jonathan Tripathy:
> > > > > Hi Michael,
> > > > >
> > > > > Thanks for your email.
> > > > >
> > > > > This is just an idea that I have floating around in my head that
> > > > > maybe I'd like to rent out some VPSs to customers, just to utilise my
> > > > > machine which will be sitting in a co-lo nearly idle.
> > > > >
> > > > > I'd give out VPSs with 256MB RAM and probably 5Mbps connection speed.
> > > > >
> > > > > So the answer is, I don't know what will be running on them, however
> > > > > I could write up an "acceptable use policy", as well as use some
> > > > > throttling/scheduling?
> > > > >
> > > > > Thanks
> > > > >
> > > > > On 06/06/10 19:39, Michael Schmidt wrote:
> > > > > > Hi Jonathan,
> > > > > >
> > > > > > the question is, what a kind of VM?
> > > > > > You can over-utilize a much greater machine with one VM.
> > > > > > Or on the other side, you can run 40 VMs on a shorter machine.
> > > > > >
> > > > > > Each ressource can be a bottleneck
> > > > > >
> > > > > > - Memory - this is realy easy to calculate: Avaiable minus 768MB
> > > > > > (Reserved for Dom0 should be enugh in this case).
> > > > > > - CPU - Here we need a VM statistic
> > > > > > - Disk Bandwidth - Here we need a VM statistic, but in the most
> > > > > > cases not the bottleneck
> > > > > > - Disk IOPS - Here we need a VM statistic, in the most cases the
> > > > > > botelneck
> > > > > >
> > > > > > What a kind of VMs you plane to run?
> > > > > > Webservers / mailservers / database-servers ...?
> > > > > >
> > > > > > Best Regards
> > > > > >
> > > > > > Michael Schmidt
> > > > > >
> > > > > > Am 06.06.10 00:54, schrieb Jonathan Tripathy:
> > > > > > > Hi Everyone,
> > > > > > >
> > > > > > > I have a Dell R210 server which has a Xeon X3430 Quad Core CPU
> > > > > > > (2.4Ghz x 4) with 8GB of RAM. I intend to use the H200 controller
> > > > > > > in a RAID1 setup
> > > > > > >
> > > > > > > How many VMs do you think I'd be able to run on this machine? Is 20
> > > > > > > pushing it?
> > > > > > >
> > > > > > > I'd say most (if not all) guests would be in PV mode.
> > > > > > >
> > > > > > > Thanks
> > > > > > >
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