MYTHBUSTING GOES VIRTUAL
MATTIAS SUNDLING
ERIC SLOOF
MYTHBUSTING GOES VIRTUAL
Eric Sloof
Mattias Sundling
VMware Certified Instructor
NTPRO.NL
@esloof
Evangelist
Dell Software
@msundling
AGENDA/MYTHS
1.
2.
3.
4.
VMware HA works out-of-the-box
VMware snapshots impacts performance
Disk provisioning type doesn’t affect performance
Always use VMware tools to sync the time in your VM
MYTH 1
VMware HA works out-of-the-box
MOST CONFIGURED ADMISSION CONTROL POLICY
ENABLING VMWARE HIGH AVAILABILITY
HOST FAILURES A CLUSTER TOLERATES
ESX01
ESX02
Shared storage – vm.vmdk
ESX03
DEFAULT MINIMUM SLOT SIZE
VM1
VM2
VM3
VM4
32 MHz
69 MB
• If you have not specified a CPU
reservation for a virtual machine, it
is assigned a default value of
32MHz.
• When the memory reservation is 0,
the slot size equals the virtual
machine overhead.
VM..n
SLOT SIZE BASED ON RESERVATION
VM1
VM2
VM3
VM4
512 MHz
1093 MB
• vSphere HA calculates the CPU and
memory slot size by obtaining the
largest CPU and memory
reservation of each powered-on
virtual machine.
VM…n
HA ADVANCED SETTINGS
• das.slotmeminmb
• das.vmmemoryminmb
Memory
reservation
SLOT
• das.slotcpuinmhz
• das.vmcpuminmhz
CPU reservation
SLOT
SPECIFY A FIXED SLOT SIZE EXPLICITLY
VMS REQUIRING MULTIPLE SLOTS
VM1
Slot size
VM2
VM3
VM4
VM5
VM6
512 MHz
512 MB
Reservation
• You can also determine the risk
of resource fragmentation in
your cluster by viewing the
number of virtual machines that
require multiple slots.
• VMs might require multiple slots
if you have specified a fixed slot
size or a maximum slot size
using advanced options.
FRAGMENTED FAILOVER CAPACITY
ESX1
ESX2
Shared storage – vm.vmdk
ESX3
WORST CASE SCENARIO
ESX01 3.6 GHz
16 GB
ESX02 3.6 GHz
16 GB
Shared storage – vm.vmdk
ESX03 3.6 GHz
32 GB
KEEP HOSTS THE SAME SIZE
Host memory:
3 * 16 GB
Host memory:
2 * 16 GB
1 * 32 GB
PERCENTAGE OF CLUSTER RESOURCES RESERVED
ESX01
ESX02
Shared storage – vm.vmdk
ESX03
PERCENTAGE RESERVED AS FAILOVER CAPACITY
ADMISSION CONTROL BASED ON RESERVATIONS
• vSphere HA uses the actual
individual reservations of the
virtual machines.
• The CPU component by
summing the CPU reservations
of the powered-on VMs.
COMPUTING THE CURRENT FAILOVER CAPACITY
• If you have not specified a CPU
reservation for a VM, it is
assigned a default value of
32MHz
RESOURCES RESERVED IS NOT UTILIZATION
• The Current CPU Failover
Capacity is computed by
subtracting the total CPU
resource requirements from the
total host CPU resources and
dividing the result by the total
host CPU resources.
PERCENTAGE RESERVED ADVANCED SETTING
• The default CPU
reservation for a VM can
be changed using the
das.vmcpuminmhz
advanced attribute
• das.vmmemoryminmb
defines the default
memory resource value
assigned to a VM
WHAT ABOUT THE WEB CLIENT
SPECIFY FAILOVER HOSTS ADMISSION CONTROL POLICY
ESX01
ESX02
Shared storage – vm.vmdk
ESX03
SPECIFY FAILOVER HOSTS ADMISSION CONTROL POLICY
• Configure vSphere HA to
designate specific hosts as the
failover hosts
THE FAILOVERHOST
To ensure that spare capacity is available on a failover host, you are
prevented from powering on virtual machines or using vMotion to
migrate VMs to a failover host.
Also, DRS does not use a failover host for load balancing
If you use the Specify Failover Hosts admission control policy and
designate multiple failover hosts, DRS does not attempt to enforce VMVM affinity rules for virtual machines that are running on failover hosts.
STATUS OF THE CURRENT FAILOVER HOSTS
Green - The host is connected, not
in maintenance mode, and has no
vSphere HA errors. No powered-on
VMs reside on the host.
Yellow - The host is connected, not
in maintenance mode, and has no
vSphere HA errors. However,
powered-on VMs reside on the host.
Red - The host is disconnected, in
maintenance mode, or has
vSphere HA errors.
MYTH BUSTED
• VMware High Availability needs to be configured
• Be careful with reservations
• Always check run-time information
MYTH 2
VMware snapshots impacts performance
WHAT IS A SNAPSHOT?
• Preserves state and data of a VM at a specific point in
time
• Data includes virtual disks, settings, memory (optionally)
• Allows you to revert to a previous state
• Typically used by VM admins when doing changes and
by backup software
• ESX3, ESX(i)4 had issues with deleting snapshots
• ESXi5 improved snapshot consolidation
WHAT IS A SNAPSHOT?
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
LOCKS
• Locks are necessary when creating, deleting and growing
snapshot, power on/off, create VMDK
• ESX(i)4 used SCSI-2 reservation
– Locks entire LUN
LOCKS
• ESXi5 uses Atomic Test & Set (ATS) VAAI primitive
– Locks only individual VM
– Requires VAAI enabled array and VMFS-5
PERFORMANCE
• Locking
– ATS increase performance up to 70% compared to
SCSI-2 reservation
• Normal operations
– Snapshot age
– Number of snapshots
– Snapshot size
• Be careful with snapshots in production!
MYTH NOT BUSTED
• Improvements to snapshots management and locking
• Snapshots still have impact on performance
MYTH 3
Disk provisioning type doesn’t affect performance
DISK TYPES
BLOCK ALLOCATION
Written Blocks
Block
VMDK File Size
Block
Thick Provision Lazy Zeroed
VMDK
Written Blocks
Block
VMDK File Size
VMDKVMDKVMDK
Written Blocks
Block
VMDK File Size
Block
Block
Block
VMDK
Block
Block
Thin Provision
Thick Provision Eager Zeroed
THE ISCSI LABORATORY
• Iomega StorCenter px6-300d with 6 SATA 7200 Disks
• Windows 2008 R2
4096 MB – 1 vCPU
Hardware Version 9
• VMware vSphere 5.1
• Single Intel 1GB Ethernet
• Cisco 2960 switch
MTU Size 1500
3 DIFFERENT DISKS
• Thick Provision Lazy Zeroed
• Thin Provision
• Thick Provision Eager
Zeroed
THICK PROVISION LAZY ZEROED
Average Write 13.3 MB/s - Access time: 44.8 ms
THIN PROVISION
Average Write 13.7 MB/s - Access time: 46.8 ms
THICK PROVISION EAGER ZEROED
Average Write 86.6 MB/s - Access time: 9.85 ms
COMPARISION
THICK PROVISION LAZY ZEROED
Average Write 13.3 MB/s - Access time: 44.8 ms
THIN PROVISION
Average Write 13.7 MB/s - Access time: 46.8 ms
THICK PROVISION EAGER ZEROED
Average Write 86.6 MB/s - Access time: 9.85 ms
MIGRATION
• Storage vMotion is able to migrate the disk format of a
Virtual Machine
MYTH BUSTED
• Thin and Lazy Zeroed disks have the same speed
• Once allocated, these disks are as fast as Zeroed disks
• Thick Provision Eager Zeroed offer best performance
from first write on
MYTH 4
Always use VMware tools to sync the time in your VM
TIME SYNC PROBLEMS
• VMs have not access to native physical HW
timers
• Scheduling can cause time to fall behind
• CPU / Memory overcommit increases risk
• People are mixing different time sync options
VMWARE TOOLS
• ESX(i) 4 and prior – not possible to adjust time
backwards
• ESXi 5 – Improved time sync to be more accurate
and can also adjust time backwards
• Enable/Disable periodic sync in VMware Tools GUI,
vCenter or VMX file
VMWARE TOOLS
• Default periodic sync interval is 60 sec
• Sync is forced even when periodic sync is disabled:
– Resume, Revert Snapshot, Disk Shrink and
vMotion
• In order to disable completely configure vmx file
– Testing scenarios
tools.syncTime = FALSE
time.synchronize.continue = FALSE
time.synchronize.restore = FALSE
time.synchronize.resume.disk = FALSE
time.synchronize.shrink = FALSE
time.synchronize.tools.startup = FALSE
time.synchronize.resume.host = FALSE
GUEST OS SERVICES
• Windows (W32Time service)
– Windows 2000 uses SNTP
– Windows 2003+ uses NTP and provides better sync
options and accuracy
– Domain joined VMs sync from DC
– Use Group Policy to control settings
• Linux (NTP)
– Configure ntpd.conf
– Start ntpd
• chkconfig ntpd on
• /etc/init.d/ntpd start
BEST PRACTICES
• ESX(i) hosts:
– Configure multiple NTP servers
– Start NTP Service
• Virtual Machines:
– Disable VMware Tools periodic sync
– DC: Configure multiple NTP servers (same as ESX(i)
host)
– Domain joined will sync with DC
– If not domain joined then configure W32Time or NTP
manually
• Do not use both VMware Tools periodic sync and Guest
OS time sync simultaneously!
MYTH BUSTED
• Use W32Time or NTP
• Do not use VMware Tools period sync
SUMMARY
• Myth 1: VMware High Availability needs to be
configured, be careful with reservations and always
check run-time information
• Myth 2:Improvements to snapshot management and
locking but still performance impact
• Myth 3: Use Thick Eager Zeroed disks for best I/O
performance
• Myth 4: Use W32Time or NTP to sync time instead of
VMware Tools
VMWORLDTV
• http://www.youtube.com/VMworldTV
QUESTIONS
Eric Sloof
VMware Certified Instructor
NTPRO.NL
esloof@ntpro.nl, @esloof
Mattias Sundling
Evangelist
Dell Software
mattias_sundling@dell.com, @msundling