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Re: [Xen-users] Please help estimate number of the domUs

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 пишет:
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 trying
the ones that ZFSBuild uses from
http://www.zfsbuild.com/pics/Graphs/Iometer-config-file.zip . That zip
file contains an IOMeter.icf file.  More details about those benchmarks
are 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 a
very good idea what level of real world performance to expect.

Here are some InfiniBand based benchmarks using that the ZFSBuild
IOmeter file:

Here are some graphs of single ethernet port benchmarks: (comparing some
hardware from 2010 with hardware from 2012)

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, 8GB
maximum 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 пишет:
You should measure the performance of the SAN using something like
IOmeter (running IOmeter on the hardware you plan to run XenServer or
XCP on).  Assuming you configure those drives in RAID10, I would guess
that 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 and
write 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 sluggish
performance.  I don't think the SAN you listed can deliver enough IOPS
to 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 пишет:
You will probably run out of disk IO before you run into any hard
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
How many IOPS does your SAN deliver over your chosen network

On 1/13/2013 9:03 AM, Andrey wrote:
Sure, will try. I see in XenServer 6.1 FAQ that maximum supported
number of guests is 150 and it requires increasing dom0_mem to max
4096. 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. It
seems that it is more realistic number although some resources note
maximum 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 пишет:
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
with typical load and get practical info.

What about network capacity? Does this math implies to the network
resources? Should we shape the DomUs bandwidth to prevent network
overload? Can CPU be bottleneck in this configuration?

The math I did was to show you some internal infrastructure limits
I know.

CPU / network overloading is another topic. TBH I haven't done
tests on CPUs and network.

And whether you will hit any bottlenecks in CPU / network or not
closely to your use case. Boot up DomUs and do some typical
workload is
a good idea.


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