VSP3067Mythbusters Goes Virtual

Name, Title, Company

Mythbusters Goes Virtual

Mattias SundlingEvangelist, Quest Software

Eric SloofVMware Certified Instructor, NTPRO.NL

Introduction

• vSphere evolves with every release.• Things that used to be true aren't true

anymore.• Engage in virtualization communities and

social media to get up to speed.

Agenda/Myths

1) iSCSI RDMs have superior performance over VMFS.

2) CBT causes significant overhead on your VMs.3) Resource Pools should always be used to

categorize and allocate resources to VMs.4) LSI SCSI is always better than Paravirtual SCSI.

Myth 1:iSCSI RDMs have superior performance over VMFS

What is a RDM

• A RDM is a symbolic link. • When a LUN is opened for access, the mapping file is read to

obtain the reference to the raw LUN.• Thereafter, reads and writes go directly to the raw LUN rather

than going through the mapping file.

RAW LUN

VMFS volume

VMkernel and Storage• Physical Compatibility

mode RDM

• Virtual mode RDM

• Regular VMDK on VMFS

• Logical device IO scheduler

• vStorage APIs

• Adapter IO schedulerand Linux emulation

The iSCSI Laboratory

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

• Windows 2008 R24096 MB – 1 vCPUHardware Version 8

• VMware vSphere 5• Single Intel 1GB Ethernet• Cisco 2960 switch

MTU Size 1500

Results Passmark PerformanceTest

• RDM Physical• RDM Virtual• VMDK on VMFS• Microsoft software

ISCSI initiator

Myth Busted• 1 Gigabit/sec (Gbps) = 112.16 MB/s.• Use VMFS datastores whenever possible.• VMFS is optimized for storing and accessing large files.

Only Use RDMs if your VM

• is performing SAN snapshotting.• is clustered to a physical machine using MSCS.• has large amounts of data (64 TB) that you do not want

to convert into a VMDK (2 TB).

Myth 2:CBT causes significant overhead on your VMs

What is CBT?• Driver inside VMkernel• Identifies change blocks within virtual

disks• Block size based on VMDK size• Backup window and host resources

significantly reduced• Requirements: vSphere 4+ and

Virtual HW v7+• Limitations: pRDM, iSCSI within VM• Enable through vCenter or backup

application

CBT Driver

CBT overhead

• Memory– Max 256 KB / Disk (2TB)– 0.125 KB / GB VMDK

• CPU– Turning on a bit in bitmap when an I/O request completes

• Storage– Space

• .ctk file 0,5 MB / 10 GB VMDK– I/O

• Every time disk gets closed, change tracking info written to disk

Test/Result

• Very little overhead CPU, Mem, Storage• Could not measure it, except .ctk file• No negative impact on disk I/OCBT Disabled CBT Enabled

Myth Busted

• CBT overhead is very small• Backup window and host resources reduced

significant• Always use CBT if your backup solution supports it

Myth 3:Resource Pools should always be used to categorize and allocate resources to VMs

Resource Settings• CPU – Shares, Reservation, Limit.• Memory – Shares, Reservation, Limit.

vApp Resource Pool VM

Sibling CPU Shares Value

• vApp = 4000

• Resource Pool= 4000

• VM = number of vCPU * 1000

Sibling Memory Shares Value

• vApp = 163840

• Resource Pool = 163840

• VM = Mem MB * 10

The Laboratory

Root Resource Pool 24 Ghz

6 Ghz6 Ghz6 Ghz6 Ghz

VM 4000 Shares6 Ghz

1.5 Ghz0.5 Ghz0,75 Ghz6 Ghz

RP 4000 Shares6 Ghz

RP 4000 Shares6 Ghz

vApp 4000 Shares6 Ghz

Myth Busted

If you want to

• use Resource Pools, do your math!

• group VMs in a container use the blue folders!

• have apple (VM) and orange (vApp) siblings take care of them!

Myth 4:LSI Logic SCSI is always better than PVSCSI

What is PVSCSI?

• Paravirtual SCSI– Introduced in vSphere 4, improved in vSphere 4.1– Designed for high performance (+12%)– Requires less resources on vSphere Host (-18%)– Supports only Win 2003+,

RHEL5+, SUSE Linux Enterprise 11 SP1+, Ubuntu 10.04 +, Linux 2.6.33+

– Virtual HW v7+

Test Result LSI Logic vs. PVSCSILSI Logic PVSCSI

Host CPU utilization90MB/s – 60 000 IOPS

• Very similar disk throughput

• Lower Host CPU Utilization for PVSCSI

Myth Busted

• PVSCSI is equal or faster than LSI SCSI• PVSCSI requires less Host resources• Used to have more limitations • PVSCSI is better in all ways so why aren´t we using it

on all supported VMs?• Takes time to change behaviour

Summary

• VMFS is better than RDMs• CBT has very little overhead• Do your math when using sibling RPs• PVSCSI is equal or faster and requires less

resources than LSI SCSI

BUT…

References• CBT

– https://www.vmware.com/support/developer/vddk/vadp_vsphere_backup12.pdf

• PVSCSI– http

://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1017652

– http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1010398

– http://blogs.vmware.com/performance/2009/05/350000-io-operations-per-second-one-vsphere-host-with-30-efds.html

– http://www.vmware.com/pdf/vsp_4_pvscsi_perf.pdf– http://www.vmware.com/pdf/Perf_Best_Practices_vSphere4.1.pdf

Questions

?

Mattias SundlingEvangelist, Quest Softwaremattias.sundling@quest.com, @msundling

Eric SloofVMware Certified Instructor, NTPRO.NLesloof@ntpro.nl, @esloof