Some things never change, or do they? vSphere is getting new and improved features with every release. These features change the characteristics and performance of the virtual machines. If you are not up to speed, you will probably manage your environment based on old and inaccurate information. The Mythbusting team has collected a series of interesting hot topics that we have seen widely discussed in virtualization communities, on blogs and on Twitter. We’ve put these topics to the test in our lab to determine if they are a myth or not.

1. Mythbusting Goes Virtual
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2. Why We Need To Bust Some Myths
• vSphere evolves
• Old beliefs are no longer true
• Keep current on the latest virtualization news
and best practices with…
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#VSVC5353 Mythbusting Goes Virtual

3. The Myths
1.
Snapshots have no performance impact
2.
Distributed vSwitch offers better performance than standard vSwitch
3.
VAAI enabled arrays can run unlimited number of VMs per LUN
4.
iSCSI offers better performance than NFS
5.
Reservations always increase performance
6.
Multiple vCPUs are always better than single
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#VSVC5353 Mythbusting Goes Virtual

4. Myth 1:
Snapshots have
no performance
impact
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5. What is a Snapshot?
• Preserves state and data of a VM at a specific point in time
• Data includes virtual disks, settings and memory (optionally)
• Allows you to revert to a previous state
• Typically used when doing changes and by backup software
• ESX 3, ESX(i) 4 had issues with deleting snapshots
• ESXi 5 improved snapshot consolidation
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#VSVC5353 Mythbusting Goes Virtual

6. Snapshot File Types
File
Description
.vmdk
Original virtual disk
delta.vmdk
Snapshot delta disk
.vmsd
DB file with relations
between snapshots
.vmsn
Memory file
• Snapshot grows in 16MB chunks
– Requires locking
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#VSVC5353 Mythbusting Goes Virtual

7. Locks – Prior to ESXi 4.1
• Locks are necessary when creating, deleting and growing snapshots,
power on/off, create VMDK and vMotion
• Used SCSI-2 reservation
– Locks entire LUN
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8. Locks – ESXi 5
• Uses Atomic Test & Set (ATS / hardware assisted locking) VAAI primitive
– Locks only individual VM
– Requires vSphere Enterprise, VAAI enabled array and VMFS-5
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9. Performance
• Locking
– ATS increase performance up to 70% compared to SCSI-2
reservation
• Normal operations
– Number of snapshots
– Snapshot age
– Snapshot size
• Be careful with snapshots in production
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10. Myth: Snapshots have no performance
impact
• Improvements to snapshots management and locking
• Snapshots still have impact on performance
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11. Myth 2:
Distributed
vSwitch offers
better
performance than
standard vSwitch
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12. vSphere Standard Switch (vSS)
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13. vSphere Distributed Switch (vDS)
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14. vDS Benefits
• Central control of virtual switch port
configuration, portgroup naming, etc
• Link Aggregation Control Protocol
(LACP)
• Health check, rollback/recovery
• RSPAN/ERSPAN
• NIOC, PVLAN, bi-directional traffic
shaping, network vMotion
• SR-IOV support
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15. Putting It To The Test
• Create two VMs on two hosts
– Using vSS and vDS
• Perform network data transfers using VM,
connected through vSS then through the vDS
• Compare the results
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16. Test Results
• Surprisingly, test results showed that data transfer times were
roughly 100Mbps FASTER when using vSS
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17. Myth: Distributed vSwitch offers better
performance than standard vSwitch
• vDS and VSS offer similar performance
• vDS offers many more capabilities and much greater management
efficiency
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18. Myth 3:
VAAI enabled
arrays can run
unlimited number
of VMs per LUN
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19. VAAI Summary and Configuration
Maximums
• Hardware assisted locking can increase performance up to 70%
compared to SCSI-2 reservation
• Requires vSphere Enterprise, VAAI enabled array and VMFS-5
Configuration Maximums
• LUN Size: 64 TB
• VMs per Host : 512
• LUNs per Host (FC & iSCSI): 256
• NFS Mounts per Host: 256
• Powered On VMs per VMFS datastore: 2048
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20. Putting It To The Test
• 2 ESXi hosts, vSphere 5.1, 32 VMs, IOmeter
• Case 1: 8*8 TB datastores without VAAI
• Case 2: 1*64TB datastore with VAAI
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21. Test Results
IOPS
25000
20000
15000
IOPS
10000
5000
0
1
2
Throughput
800
600
400
MBps
200
0
1
21
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22. Considerations for Datastore Consolidation
• Default 1 path per LUN
• Check if MPIO is supported
• LUN Queue Depth
• Disk.SchedNumReqOutstanding (DSNRO)
• All eggs in one basket – DR
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23. Myth: VAAI enabled arrays can run
unlimited number of VMs per LUN
• Hardware assisted locking helps reducing locking and latency
• Increases VMs per LUN to a certain degree but not unlimited
• Carefully look at other components end-to-end to maximize
performance and density
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24. Myth 4:
iSCSI offers better
performance than
NFS (for
virtualization)
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25. iSCSI vs. NFS Features And Functions
• iSCSI = block based
• iSCSI = SAN
• Multipath included
• Hardware iSCSI is an option
• Both use Ethernet network and
offer jumbo frames
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• NFS = file based
• NFS = NAS
• No built in HA or load
balancing (relies on network)
• Easier to configure
• More readily available
• Shared filesystem
#VSVC5353 Mythbusting Goes Virtual

26. Putting It To The Test
• Create 2 datastores, 1 NFS, 1 iSCSI (software)
• Both datastores are connected to the same
shared storage
• Create a single VM on a host that has
connections to both datastores
• With the VM on the iSCSI datastore, perform IO
tests
• svMotion the VM to the NFS datastore, and
perform IO tests
• Compare the results
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27. Test Results
iSCSI vs. NFS Test Results from Jason Boche’s Lab
1600
1400
1200
1000
800
iSCSI (SW)
NFS
600
400
200
0
1
27
2
3
4
5
Notes:
Tests are a composite
score based on seq
read, seq, write, and
random seek + rw for a
period of 5 minutes
each
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28. Myth: iSCSI offers better performance than
NFS (for virtualization)
• Both NFS and iSCSI are solid options for
vSphere storage
• Ensure you are knowledgeable of the
pros and cons offered by each to make
the right choice for your company
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29. Myth 5:
Reservations
always increase
performance
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30. Reservations
• Specifies the guaranteed
minimum allocation for a
specified resource
• Insurance that resources are
available
• Default is 0 (no reservation)
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31. Memory Reservation
• VM with memory reservation that hasn´t accessed its full memory
can be used by other VMs
– Different OS handles memory differently
• After VM has accessed its full reservation, the memory can´t be used
by other VMs, even if the VM isn´t using it
• Memory is wasted
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32. CPU Reservation
• VM with CPU reservation of 5 GHz that is idle
• Other VMs cannot reserve these 5 GHz but they can use it
• CPU is not wasted
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33. Reservations Pros and Cons
Pros
• Can improve performance when host is overcommitted
• Can improve performance even when host isn't overcommitted
Cons
• Can affect performance for other VMs
• Can affect admission control
– Host
– High Availability
– Distributed Resource Scheduler
• Can reduce VM density
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35. Myth: Reservations always increase
performance
• Reservations don´t always provide better performance
• Insurance if host is overcommitted
• Can increase performance for Java workloads
• Use reservations for business critical applications only with caution
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36. Myth 6:
Multiple vCPUs
are always better
than single
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#VSVC5353 Mythbusting Goes Virtual

37. Multiple vCPU Background
Is “more” always “better”? Melvin the Monster VM thinks so…
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38. Multiple vCPU and Multiple Sockets
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39. Putting It To The Test
• Create 1 VM with 1 vCPU
• Run single and multi-threaded CPU tests
• Power off the VM and add multiple vCPUs
• Re-run single and multi-threaded CPU tests
• Compare the results
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#VSVC5353 Mythbusting Goes Virtual

40. Test Results
numbers are in millions of I/Os per second
1vCPU
4vCPU
Multi threaded app
Single threaded app
0
40
1000
2000
3000
4000
5000
6000
7000
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41. Myth: Multiple vCPUs are always better than
single
• Tests show that multiple vCPUs give a massive performs boost IF you
have an application that can take advantage of it
• A single threaded app just needs one vCPU
• KNOW YOUR APP
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42. Summary
1.
Snapshots can have performance impact
2.
Distributed vSwitch and Standard vSwitch offer similar
performance
3.
VAAI enabled arrays increase VM density per LUN
4.
iSCSI and NFS offer similar performance
5.
Reservations can increase performance
6.
Multiple vCPUs are better for multithreaded applications
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#VSVC5353 Mythbusting Goes Virtual

43. Thank you for your
participation
Join the conversation…
More conversations on line
Michele Ballinger
@ballingertweets
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