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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-users] Please help estimate number of the domUs
I have not personally seen a performance issue related to the number of VMs per LUN, but I have never tried 100 VMs per LUN. Certain SANs may implement the access queues in such a way to effectively cause 20 VMs to be a sweet spot like that article describes, but I suspect it would vary from one SAN to the next. Even though I have not run into that issue, it is very possible that article is correct. Especially in your case with 100 VMs, you may want to follow the advice in that article and split your VMs across several LUNs. What ever you do, always leave extra room in each LUN for special operations (such as snapshots, migrations, etc). For example, any time you need to migrate storage with XCP/XenServer, you will need a lot of disk space available on both the target and source SRs to complete the task. The extra disk space will be allocated and used behind the scenes, but the operation will fail if there is not enough disk space available. If your VMs are each 30GB, make sure you plan to leave 30-60GB of additional free space in each LUN to make sure you have room for those operations. On 1/16/2013 11:31 PM, Andrey wrote: Thank you very much for the clear and detailed explanations. Many things became clear to me now. I really appreciate that.As for the number of LUNs I've read http://blogs.citrix.com/2011/06/01/sizing-luns-a-citrix-perspective/article where it's recommended to create separate LUN for each 20-30 VMs.So for example for 100 VMs there can be 4 LUNs each stores 25 VMs. Initially we'll have one XCP host, so 3.6TB with the average size of the VM = 30GB there will be 5 LUNs/SRs each 720GB though it complicates managing VMs a little. Does it make sense for the performance?17.01.2013 01:07, admin@xxxxxxxxxxx ÐÐÑÐÑ:For web server VPS instances, I usually see real world performance trend most closely with the 4k random 67% write 33% read tests. The reason those VPS instances tend to skew toward vastly more writes than reads is the http log files. The most heavily access web pages are cached in memory in the VPS, so there are fewer read operations hitting the SAN. The logs still need to be written, though. The log file are being written in random bursts when there are lots of different sites, even though the individual log files are sequential. These results for your SAN were 4915 to 6317 (depending on queue depth). This is the upper end of my initial guess for your SAN (my guess was 2000 to 5000). Based on your benchmarks, your SAN can deliver about 5000 IOPS in the test that I personally think most closely resembles the real world usage pattern for a web server running in a VPS. Note, the "4k random 67%read33%write" is actually mislabeled. It should say "4k random 67% write 33% read". The wild card is database access, especially if you hosting databases for people with a variety of skill levels. If the tables are well designed and properly indexed, then there will be very little disk access. If the tables are poorly designed and not indexed properly, there will be a lot of disk access. I have seen some customer sites that need hundreds of IOPS just to service a tiny amount of traffic due to poor database design. On the other hand, I have seen a well designed (and very well indexed) DB that averages 40 IOPS while servicing millions of queries per day. The sequential IO tests are an excellent test for how fast you will be able to copy large files, which is important when you are migrating a VPS between multiple SAN targets. Generally speaking, sequential access performance is usually far less important than random access performance. Random IO is far more common than sequential. And when you run a bunch of VPS instances, even sequential IO becomes random IO simply because of all of the VPS instances accessing different areas of the storage volume. So I tend to look more at the random performance. If you have multiple pools, create a separate LUN for each pool. If you have only one pool, just create one LUN. This is true regardless of how many physical XCP/XenServer nodes exist within that pool. XCP and XenServer are smart enough to make sure each VPS can only access its own data blocks even when many VPS share the same LUN. If you have only one pool, simply create one LUN. Then on the XCP/XenServer side, add that iSCSI target as a storage repository. Then create your VPS instances on the storage repository. XCP/XenServer will handle everything else under the hood. You don't need to manually install a cluster aware file system or use a separate LUN per VPS. On 1/16/2013 6:55 AM, Andrey wrote:Ok. I performed tests with icf in Iometer-config-file.zip file (8 workers and 120 GB max file size) on RAID1+0 LUN, please see attached. In this tests IOPS are much smaller. What is the real word performance then? I'm little confused. Also is that right that I should not create one big LUN for VMs and create few LUNs with the LUN size = (size of 20-30 VMs)*(average size of VM) for better performance? 16.01.2013 02:07, admin@xxxxxxxxxxx ÐÐÑÐÑ:Those numbers are higher than I would have expected given the hardware you listed. For mixed random access, I expected your hardware would have delivered 2000 to 5000, not 49747. Of course, I test with 100% random and 67% writes. You were testing with 60% random and 35% writes. There could be considerable caching involved (especially with read tests), but it is hard to say without more data points.If you want to run more benchmarks with IOmeter, I would suggest tryingthe ones that ZFSBuild uses from http://www.zfsbuild.com/pics/Graphs/Iometer-config-file.zip . That zipfile contains an IOMeter.icf file. More details about those benchmarksare at http://www.zfsbuild.com/2012/12/14/zfsbuild2012-benchmark-methods/Anyway, I am a lot more familiar with the benchmarks from ZFSBuild. If you run those benchmarks and post those results, then I could give you avery good idea what level of real world performance to expect. Here are some InfiniBand based benchmarks using that the ZFSBuild IOmeter file:http://www.zfsbuild.com/2012/12/15/zfsbuild2012-infiniband-performance/Here are some graphs of single ethernet port benchmarks: (comparing somehardware from 2010 with hardware from 2012)http://www.zfsbuild.com/2012/12/14/zfsbuild2012-performance-compared-to-zfsbuild2010/On 1/15/2013 2:33 PM, Andrey wrote:Just finished measuring SAN performance with IOmeter(http://vmktree.org/iometer/OpenPerformanceTest.icf and 5 minutes each test) on RAID10 (data, 16GB maximum test file) and RAID50 (backup, 8GBmaximum test file) both 3.6TB with one ext4 partition. SAN is configure in dual-path configuration and server has multipath configured with 2 HBA adapters. Here are the results: RAID 5+0: ----------------------------------------------------------------- | Test name | Avg iops | AvgMBps | ----------------------------------------------------------------- | Max Throughput-100%Read | 47528 | 1485 | | RealLife-60%Rand-65%Read | 24760 | 193 | | Max Throughput-50%Read | 6959 | 217 | | Random-8k-70%Read | 26612 | 207 | ----------------------------------------------------------------- RAID 1+0: ----------------------------------------------------------------- | Test name | Avg iops | AvgMBps | ----------------------------------------------------------------- | Max Throughput-100%Read | 44031 | 1375 | | RealLife-60%Rand-65%Read | 49474 | 386 | | Max Throughput-50%Read | 43002 | 1343 | | Random-8k-70%Read | 49930 | 390 | ----------------------------------------------------------------- Caching is in action or else? 13.01.2013 23:52, admin@xxxxxxxxxxx ÐÐÑÐÑ:You should measure the performance of the SAN using something likeIOmeter (running IOmeter on the hardware you plan to run XenServer or XCP on). Assuming you configure those drives in RAID10, I would guessthat SAN would deliver about 2,000 to 5,000 IOPS. If you use RAID5(please don't), then you will see far less IOPS during mixed read andwrite tests.If you want to deploy 100 VMs onto that SAN, then each VM is only have to have 20-50 IOPS (assuming RAID10). The performance in each VM will be less than fantastic. If the VMs need to do any IO intensive tasks,the owners of the VMs are probably going to complain about sluggishperformance. I don't think the SAN you listed can deliver enough IOPSto satisfy 100 VMs. On 1/13/2013 12:17 PM, Andrey wrote:Well, storage is the direct-connect HP P2000 G3 FC dual-controller array with 600GBx24 disks in dual-path configuration (two HBA ports -> two controllers ports). I guess it is quite enough. 13.01.2013 20:45, admin@xxxxxxxxxxx ÐÐÑÐÑ:You will probably run out of disk IO before you run into any hard limits in XenServer or XCP. What type of SAN are you going to use? What type of network interconnect will you use to link your XenServer/XCP nodes to your SAN? How many IOPS does your SAN deliver over your chosen network interconnect? On 1/13/2013 9:03 AM, Andrey wrote:Sure, will try. I see in XenServer 6.1 FAQ that maximum supportednumber of guests is 150 and it requires increasing dom0_mem to max4096. It's obvious that internal limits are not quite realistic so it will be good result for me if we able to run at least 100 guests. Itseems that it is more realistic number although some resources notemaximum number of VMs as 4-10 per CPU core (so 32-80 in my case). But in all these cases 192 GB RAM would be redundant I think. With regards, Andrey 11.01.2013 16:43, Wei Liu ÐÐÑÐÑ:On Fri, 2013-01-11 at 12:24 +0000, Andrey wrote:Thank you for the answer I'm really consider the case with creating as many DomUs as possible with typical load and get practical info. What about network capacity? Does this math implies to the networkresources? Should we shape the DomUs bandwidth to prevent networkoverload? Can CPU be bottleneck in this configuration?The math I did was to show you some internal infrastructure limitsthat I know. CPU / network overloading is another topic. TBH I haven't done stress tests on CPUs and network. And whether you will hit any bottlenecks in CPU / network or not relates closely to your use case. Boot up DomUs and do some typical workload is a good idea. 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