How to Fail at VDI

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Welcome


Dan Brinkmann @dbrinkmann blog.danbrinkmann.comSolutions Architect, VMware vExpertLewan & Associates (Denver, CO)

How to Fail at VDI

“What business problem are we solving?”


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Business/Expectation VDI Failures

● No business problem● Desktop virtualization is not server virtualization● Saving money● Project in the hands of the vSphere administrator● No success criteria● Assume you know what users do● The same or better experience remotely as locally


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Agenda

● Compute● Storage● Guessing

To understand what causes VDI failures

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How to Fail at VDI

● Test with 5 users● Using vendor provided users/core sizing● Using vendor provided IOPs estimates● Ignore anti-virus● Ignore user profile management● Use existing desktop images for physcial PC’s● Guess


The technology failure points

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Compute

● Multi-threaded apps● Latency sensitive workloads● Hyperthreading● Latency = Health


It’s magic until it stops working

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Compute

● CPU scheduler in vSphere is entitlement/consumption based, not priority (unlike Windows)

● There is no priority in the CPU scheduler● Given equal entitlement the more a vm/world consumes

the more likely it is to be prempted by another vm/world● http://www.vmware.com/resources/techresources/10131


CPU scheduler in vSphere

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Compute with a Physical PC


CPU 1

OS/Apps/Profile

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Compute with Citrix XenApp


OS/Apps/Profile

OS/Apps/Profile

CPU 1 CPU 2

OS/Apps/Profile

OS/Apps/Profile

OS/Apps/Profile

OS/Apps/Profile

OS/Apps/Profile

OS/Apps/Profile

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Compute with VDI


CPU 1 CPU 2

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vSphere Compute


This is poor performance monitoring

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vSphere Compute


This is better performance monitoring - ESXTOP

Display Metric Threshold Explanation

CPU %RDY 10 Overprovisioning of vCPUs, excessive usage of vSMP or a limit(check %MLMTD) has been set.

CPU %CSTP 3Excessive usage of vSMP. Decrease amount of vCPUs for this particular VM. This should lead to increased scheduling opportunities.

CPU %SYS 20The percentage of time spent by system services on behalf of the world. Most likely caused by high IO VM. Check other metrics and VM for possible root cause

CPU %MLMTD 0The percentage of time the vCPU was ready to run but deliberately wasn’t scheduled because that would violate the “CPU limit” settings. If larger than 0 the world is being throttled due to the limit on CPU.

CPU %SWPWT 5 VM waiting on swapped pages to be read from disk. Possible cause: Memory overcommitment.

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vSphere Compute


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vSphere Compute


%CSTP probably driving %RDY values

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vSphere Compute


Now with fewer vCPU’s

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Summary on Compute

● Multithreading, vSMP● Not priority based● % Utilization is not the complete picture● Latency = Health● http://kb.vmware.com/selfservice/microsites/search.do?

language=en_US&cmd=displayKC&externalId=1017926


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Storage

● #1 cause of performance issues in server virtualization● #1 cause of performance issues in desktop virtualization● Latency = Health

20ms - in trouble 50ms - your users hate you


The wrath of the math

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What You Need to Know

● Capacity vs performance● Random vs sequential● Average vs peak● Where it’s coming from● Most are guessing


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Storage


Spinning disk

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RAID Penalty


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The Math – RAID 5 50/50

● 500 users, Windows 7, 20 IOPs avg, 50/50 read/write RAID 5

● 500 * 20 = 10,000 IOPs – 5,000 read, 5,000 write● 5,000 write * 4 = 20,000 + 5,000 read = 25,000 IOPs● 25,000 IOPs on 15K spindles (200 IOPS) = 125 spindles


Some back of the napkin math

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vSphere Storage Latency


Guest

VMkernel

Application

Filesystem

I/O Drivers

Virtual SCSI

Filesystem

A

G

D

K

S

R

Device Queue

Application Latency

R = Physical Disk “Disk Secs/Transfer”

G = Guest Latency

K = ESX Kernel

D = Device Latency

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vSphere Storage


Performance monitoring for storage

Display Metric Threshold Explanation

DISK GAVG 20 Look at “DAVG” and “KAVG” as the sum of both is GAVG.

DISK DAVG 20 Disk latency most likely to be caused by array.

DISK KAVG 2 Disk latency caused by the VMkernel, high KAVG usually means queuing. Check “QUED”.

DISK QUED 1Queue maxed out. Possibly queue depth set to low. Check with array vendor for optimal queue depth value.

DISK ABRTS/s 1 Aborts issued by guest(VM) because storage is not responding. Can be caused when paths failed.

DISK RESETS/s 1 The number of commands reset per second.

DISK CONS/s 20 SCSI Reservation Conflicts per second. Can be caused by too many VMDKs on a datastore.

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Building for Read IOPs

● Memory - Storage controller cache, PVS● Host/Hypervisor - CBRC, Intellicache● Storage - SSD tiering / flash cache


Fairly easy

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Building for Write IOPs

● Profiles/Apps● Spinning disk● SSD tiering● Local disk● IO optimization (dedupe, serializing IO)


Much harder…and expensive

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Storage Summary

● 25,000 IOPs R5 50/50 – 125 spindles● 15,000 IOPs R10 50/50 – 75 spindles● 18,000 IOPs R10 20/80 – 90 spindles● Latency is the key metric● Write IOPs & things that cause it is #1 focus


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How does this relate to VDI failure?

● Pilot performance is great, then terrible in production● Boot storm vs login storm● Applications in gold image vs streamed● Read/write ratio is important● Anti-virus software● Existing desktop images


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Guessing

● Initial sizing● Determine peaks and when● Baseline application impact● Monitor application impact over time● Application updates/changes


You need to use tools to do this

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Project testing

● Unit/system testing● Application testing● Performance/scalability testing● Operational testing● User acceptance testing


Good to know what you are and aren’t doing

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Summary

● Understand your limited resources (compute/storage)● Don’t guess● 5 users = what kind of testing, what are you really

accomplishing?


How to Fail at VDI

Technology

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