mythbusting goes v irtual

MYTHBUSTING GOES VIRTUALMATTIAS SUNDLINGERIC SLOOF

MYTHBUSTING GOES VIRTUAL

Mattias SundlingEvangelistDell Software@msundling

Eric SloofVMware Certified InstructorNTPRO.NL@esloof

AGENDA/MYTHS

1. VMware HA works out-of-the-box2. VMware snapshots impacts performance3. Disk provisioning type doesn’t affect performance4. Always use VMware tools to sync the time in your VM

VMware HA works out-of-the-box

MYTH 1

MOST CONFIGURED ADMISSION CONTROL POLICY

WHY?

ENABLING VMWARE HIGH AVAILABILITY

HOST FAILURES A CLUSTER TOLERATES

ESX01 ESX02 ESX03

Shared storage – vm.vmdk

DEFAULT MINIMUM SLOT SIZE

• 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.

32 MHz69 MB

VM1 VM2 VM3 VM4 VM..n

SLOT SIZE BASED ON RESERVATION

• vSphere HA calculates the CPU and memory slot size by obtaining the largest CPU and memory reservation of each powered-on virtual machine.

512 MHz1093 MB

VM1 VM2 VM3 VM4 VM…n

HA ADVANCED SETTINGS

• das.slotcpuinmhz• das.vmcpuminmhz

Memory reservation

CPU reservation

SLOT

SLOT

• das.slotmeminmb• das.vmmemoryminmb

SPECIFY A FIXED SLOT SIZE EXPLICITLY

VMS REQUIRING MULTIPLE SLOTS

512 MHz512 MB

VM1 VM2 VM3 VM4 VM5 VM6

Reservation

Slot size

• 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 ESX3


WORST CASE SCENARIO

ESX01 3.6 GHz 16 GB

ESX02 3.6 GHz16 GB

ESX03 3.6 GHz32 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 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 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 VM-VM affinity rules for virtual machines that are running on failover hosts.

STATUS OF THE CURRENT FAILOVER HOSTS

Red - The host is disconnected, in maintenance mode, or has vSphere HA errors.

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.

MYTH BUSTED

• VMware High Availability needs to be configured• Be careful with reservations• Always check run-time information

VMware snapshots impacts performance

MYTH 2

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!

• Improvements to snapshots management and locking• Snapshots still have impact on performance

NOT

MYTH NOT BUSTED

Disk provisioning type doesn’t affect performance

MYTH 3

DISK TYPES

BLOCK ALLOCATION

VMDK

Block Block Block

VMDK File Size

Written BlocksThick Provision Lazy Zeroed

VMDK

Block Block Block

VMDK File Size

Written BlocksThin Provision

VMDK

Block Block Block

VMDK File Size

Written BlocksThick Provision Eager Zeroed

VMDKVMDK

THE ISCSI LABORATORY

• Iomega StorCenter px6-300d with 6 SATA 7200 Disks

• Windows 2008 R24096 MB – 1 vCPUHardware 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


THICK PROVISION EAGER ZEROED


COMPARISION




THICK PROVISION LAZY ZEROED

THIN PROVISION

THICK PROVISION EAGER ZEROED

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

Always use VMware tools to sync the time in your VM

MYTH 4

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 scenariostools.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

Mattias SundlingEvangelistDell [email protected], @msundling

Eric SloofVMware Certified [email protected], @esloof

mailto:[email protected]


https://www.twiiter.com/msundling


https://www.twiiter.com/esloof

https://www.twiiter.com/esloof

mythbusting goes v irtual

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