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Posts Tagged ‘ESX’

I needed to grab some stats from my ESX hosts for off-line analysis so I fired up my trusty ESXTOP intent on using batch mode to capture a .csv formatted output.  I started to manually select the counters I was interested in while working in ESXTOP interactive mode (you can save your selected counters to the esxtop configuration file with the ‘w’ command) and thought that there must be a better way.  I found that better way in the VMware Performance Community: http://communities.vmware.com/docs/DOC-3930.  There is now a -a switch that can be used to include ALL performance counters.  I’m sold.

I wanted detailed information, so I decided on a 15 second capture interval to run for a 2 hour window.  Here’s the command I used:

esxtop -a -b -d 15 -n 480 > /tmp/esxtopout.csv

where -a is for ALL, -b is for batch mode, -d is for delay, and -n is for the number of iterations ((60/15)*60*2).  I wrote out the results to a .csv in /tmp.  The resulting CSV weighed in at a whopping 100MB after 2 hours.

The CSV can be analyzed in Excel (pivot tables work well for this) or in Windows Perfmon.  I opened the log in Perfmon as I was after basic Min/Average/Max counters and Perfmon makes those easy to see.  When adding the CSV log to Perfmon, you are prompted to select counters.  I added all instances of Commands/sec, Reads/sec, and Writes/sec from Physical Disk (I was gathering some IOPS counts for a new storage proposal). I got a bit more than I bargained for: a mostly unresponsive Perfmon window and the ugliest darn graph I’ve ever seen.

Switching from a graph view to the report view allows you to easily view and remove specific counters that you are not interested in, or open the Properties of the data set, switch to the data tab and bulk select counters that you want to remove.  I was not interested in vmhba1:x, specific VM’s or worlds, so I killed all of those, leaving just the base iSCSI device (vmhba32 in my case).

After some cleanup the graph looked a bit better and more importantly, I was able to easily read my Min/Average/Max stats:

Here are the takeaways -

• ESXTOP is a powerful utility for performance monitoring
• All stats (-a) can result in a huge file – use it wisely in batch mode; else use interactive mode to select your counters and write them to the user-defined configuration file.  Invoke the config file with the -c option when running in batch mode.
• Consider using vscsiStats for more granular reporting.
• ESXTOP physical disk stats do not include NFS volumes.

Do you use other tools or methods to collect basic disk IO counters for storage sizing purposes?  If so, leave a comment describing your approach!

I have been meaning to write this up for a while; Scott Drummonds’ ‘Love Your Balloon Driver’ post today at his Virtual Performance blog gave me a nice reminder.  I actually caught a sneak peak at the graphs with an explanation from Scott at his instructor-led lab at VMworld 2009.  Scott calls out that the only workload they discovered suffers from balloon driver activity is Java.  The reason for Java’s problems with balloon driver activity is that Java itself runs in a VM and so the guest OS cannot properly determine which pages should be swapped out when the balloon driver calls for it.

My experiences causes me to agree with Scott and the whitepaper he cites – in a properly designed and equipped environment the balloon driver is not detrimental for most every workload to a point.   However, I recently discovered in a client site that the balloon driver can cause significant issues when the environment is poorly designed and under-sized.  Here the background:

I was called into an already established environment where the client was running on an older blade with VMware ESX 3.5.  The blade maxed out at 16GB RAM and had dual dual-core CPU’s with no hope for an upgrade.  On the blade was a single guest VM running Windows 2003 with SQL 2005, in it’s full 32-bit glory.  The VM was configured with 4 vCPU’s and 16GB of memory.  Some of you can probably already guess where this is going….

The x86 Windows guest had PAE configured, and SQL took advantage of AWE to use the additional memory beyond the 4GB limit of a 32-bit system.  Additionally, the Windows guest had the /3GB switch enabled in boot.ini.  Finally, as per SQL best practices, the ‘Lock Pages in Memory‘ permission was granted to the SQL Server service account.  What the guest was left with was 1GB of kernel mode memory and 15GB of User Mode/Extended addressable memory.

And here’s the problem.  The client was using ESX, not ESX 3.5, so the Service Console required memory.  In this case, the service console had approximately 512MB allocated to it.  Futhermore, VM’s require some overhead on ESX to run.  The memory overhead consumed by a Windows guest on ESX 3.5 with 4 vCPU and 16GB of memory is a bit more than 512MB.  On a properly sized ESX server with multiple similar guests/workloads, you could probably gain much of the overhead back through transparent page sharing; but in this case I had a 1:1 P2V ratio.  If you are any good at math you see that the environment is running about 1GB short of memory.  A quick check of the balloon driver stat in vCenter show that the balloon driver was constantly active and demanding about 1GB back from the guest… constantly.

Under normal circumstances this might not be an issue, but in this case the Windows guest was being absolutely punished.  The guest CPU’s were pegged at 100% with an excessive amount of kernel time, often indicating IO issues.  And indeed I did experience terrible disk and network performance on the guest.  At the root of the problem is this – the Lock Pages in Memory permission allows SQL to get a firm grasp on the user mode memory available to it (15GB) and lock it up.  This left the already starved (because of the 3GB switch in the boot.ini) guest kernel with it’s 1GB the only thing the balloon driver could really swap out.

The client suggested a reservation of 16GB on the VM, knowing that memory reservations prevent balloon driver activity.  I calmly asked them to back away from the keyboard as I explained how if a starved guest was bad, how much worse a starved Service Console would be.  In the end the fix was quiet easy – I convinced the customer that they should reduce the amount of memory allocated to the guest by about 1GB, enough to let the 512MB SC and the 512MB of overhead run without contention.  I was able to show them the difference between allocated and active memory in vCenter – the 1GB being surrendered was not really being actively used, SQL just had it locked up.  In fact, surrendering the 1GB of memory back to ESX breathed new life into the guest VM, bringing its performance back in line with expectations.

Ideally, I would have brought in a bigger ESX server that could serve additional VM’s, driving greater levels of efficiency across the environment.  It just wasn’t an option for the client in this case.  In the end, the problem was fixed and I was reminded just how fun it can be to explain some of these backwards sounding virtualization concepts to customers – fewer vCPU’s can lead to better performance of guests, less guest memory can fix performance issues, and increasing the quantity of similar guests on a host can drive better performance to a point because of transparent page sharing.

Stay tuned over the next few weeks as I digest and write on my VMworld experience – from VMUG activities to Paul Maritz’s press conference announcing the vCloud Express, and plenty of great sessions in between.  Like many of you, I returned from VMworld with quite a backlog of work but I’ll do my best to squeeze in some posts and tweets.

I have been pulling my hair out with a small VI3 implementation running against an IBM DS3300 iSCSI array.  Performance, for lack of a better term, sucked.  Granted, the DS3300 is not an enterprise level workhorse of a storage system, but it fit the budget.  Read performance was decent from the array, but write performance was terrible, maxing out at 10Mpbs throughput and insanely high latencies on long writes when the system was under load.  This led to some long P2V operations, poor guest performance, and some questions from the project sponsors on why I couldn’t make the environment sing.

The system was configured with a single controller with dual GigE NIC’s.  The controller had 512MB of battery backed cache (there is also a 1GB cache upgrade option available).  I wrote off some of the poor performance to a single controller with a less-than-optimal amount of cache; blamed the SAS controller to SATA disk command translation overhead; cringed at the 6 disk RAID5 configuration; and engaged in some self doubting.  I convinced the powers that be that we were IO constrained and got some funds to fill out the 3U chassis to a full 12 SATA disks, and reconfigured the array as a RAID10.  Performance gains were almost unnoticeable with these changes.  In addition, I did some basic troubleshooting of the network environment, verifying multiple paths to the storage, setting Flow Control on the switches to receive only, and double-checked my iSCSI initiator settings.  Note: The DS3300 is only supported with the ESX software initiator.  I found documentation on the DS3300 to be lacking, but did discover that the Dell MD3000i is based on the same LSI Engenio array.  Some Googling on the Dell solution led to to the ‘SMcli’ command line interface for both arrays.   The commands are slighly different for the Dell and IBM.  The links to the IBM CLI documentation were broken, so I had to do a bit of trial and error to get the commands right.  I used the Dell documentation as a starting point.  (Rant: Seriously, IBM?  Can you make your documentation any harder to get through – is it a Redbook, is it an Engineering Whitepaper, is it a support document, is it a case study – and why can I only find these with complex Google searches, not on your own product pages, and why can’t you name for documents intelligently, not with some random string of characters).

Moving on… I received an automated alert from the DS3300 about an incomplete battery learn cycle.  Using the IBM Storage Manager GUI I generated a  Storage Subsystem Profile’ from the Support tab to check the battery status.  In the profile I discovered that while write cache was enabled, it had a status of “Enabled (Suspended)”.   Ah ha!  Now I’ve got some decent Google material that led me to this: http://communities.vmware.com/thread/195838.  Hot damn I love the VMware Community Forums!

It turns out that in a single-controller configuration the setting for cache mirroring remains enabled by default.  Because there is no 2nd controller to mirror to, the array suspends write caching.  This is probably a safety thing – loss of high availability on the controllers puts data in cache at risk should the only controller fail.  I weighed my options and decided that the poor performance I was experiencing beat HA concerns, so I enabled write cache on the array using this command:

c:\program files\ibm_ds4000\client>smcli -n <ARRAYNAME> -c “set allLogicalDrives mirrorEnabled=false;”

And then followed with this for good measure:

c:\program files\ibm_ds4000\client>smcli -n <ARRAYNAME> -p <arraypassword> -c “set allLogicalDrives writeCacheEnabled=true;”

The results were immediately noticeable:

DS3300 Performance Improvement when Write Cache is Enabled - Click for a Larger View

The screen shot is from Veeam Monitor Free Edition, taken during 4 concurrent V2V operations from Hyper-V to VMware.  With the write cache fully functional, disk usage peaked at 54MBps, latency dropped to about 6ms, and my blood pressure dropped a few notches.

While poking around the CLI I also found that you can dump performance stats from the array (performance is otherwise hard to find on the thing) using this command:

C:\Program Files\IBM_DS4000\client>smcli -n <ARRAYNAME> -c “set session performanceMonitorInterval=5 performanceMonitorIterations=120;save storageSubsystem performanceStats file=\”c:\\ds3300perfstats.csv\“;”

This will give you a 10 minute record of performance from the array which you can analyze using Excel.  The Dell Enterprise Center TechCenter Wiki has a great write-up on how to efficiently analyze the data from this command here: http://www.delltechcenter.com/page/MD3000i+Performance+Monitoring, complete with a YouTube video that walks you through the process:

I am beginning to think that the DS3300 (and MD3000i) may actually be a viable starter solution for SMB’s starting out on a virtualization project.  But I would recommend the cache upgrade, 2nd controller, SAS disks instead of SATA to eliminate the SAS-to-SATA translation overhead and more faster disks instead of fewer slower disks so you can drive throughput and IOPS to a higher level.

Have any of you deployed the DS3300 or MD3000i (or the generic LSI solution)?  Do you have any performance tuning tips for these arrays?  If so, share in the comments!

VMware vExpert and fellow Northern Virginian, Ken Cline, has posted an excellent article on his Ken’s Virtual Reality blog that aims to demystify VMware networking.  The article, the first in a new series by Ken, provides an overview of networking in an ESX/ESXi environment and breaks down the intricacies of the vSwitch and VLANs.  The article comes complete with some nifty diagrams to help make sense of the topic. The timing of this article is great for me as it helps to frame my thoughts as I delve into the design of my latest VMware project on an IBM BladeCenter with IP SAN storage.

Great article, Ken!  I look forward to reading the rest of the series.