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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-users] How many guests
Hi Jonathan,for iSCSI a iSCSI storage is suggestable, or opene if you plan to run it on a x86 server. But you need dedicated lan line, a storage box with its own raid controller and cpu, memory and so on. And a iSCSI hostbus adapter (around 600€) on the xen host side. If you dont have a iSCSI HBA, you have to use the software iSCSI initiator (i dont like this piece of software, and you have iSCSI CPU Usage on your host). If you want to run just a few more disks for one server (without HA options), you dont need all this overhead. Buy additional to your xen host a SAS Raid controller with an external port (+150€). And a 12-disk JBOD (800€) and the disks (SATA / SAS). This provides you a lower TCO and a higher energy efficiency (3-4U and 450W for 60 VMs). Best Regards Michael Schmidt Am 07.06.10 09:16, schrieb Jonathan Tripathy: 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 webserversvisited 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 thatmaybe I'd like to rent out some VPSs to customers, just to utilise mymachine 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 setupHow many VMs do you think I'd be able to run on this machine? Is 20pushing it? I'd say most (if not all) guests would be in PV mode. 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