1. SUM230: Optimizing storage
across FlexCast delivery models
Alex Danilychev, PhD Angelo Oddo
Sales Engineer Sr. Sales Engineer
October 15, 2012

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Agenda

3. Typical elements of VDI design
• Blade servers
• Shared storage

4. Typical VDI challenges
• Hardware cost is 80% storage dependent
• Bulk storage purchasing impacts incremental growth
• Future scalability demands storage redesign

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Shared storage growth and user productivity
1,000
500
User Count
Cost, AU100 200
500
User Count
Productivity per user
AU – arbitrary units

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Combined productivity and storage evolution
Redesign
1,000
500
Combined
Productivity
100 200 Cost, AU
Combined
Productivity
1,000
500
Cost, AU100 200
?
Alternatives
AU – arbitrary units

7. POD Implementations

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A pod is a discrete,
homogeneous, modular unit
of data center components
Cisco
http://www.cisco.com/en/US/docs/solutions//Enterprise/Data_Center/VMDC/large_pod_design_guide/Large_Pod_Design_Guide.pdf

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Redesign
Productivity improvements with POD deployment
1,000
500
Combined
Productivity
100 200 Cost, AU
POD #1
POD #2
POD #3
1,000
500
Combined
Productivity
100 200 Cost, AU
AU – arbitrary units
No redesign

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Common POD Characteristics
• Addresses performance uncertainties through resource segmentation
• Not cost effective at low utilization
• Targets large implementations
• Cost prohibitive for small deployments
• Hardware cost per user is $1,000 or higher

11. Can we do better?

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Citrix FlexCast VM delivery options
• Single-tenant VMs:
○ VDI-in-a-Box
○ MCS (Machine Creation Services) – XenDesktop
• Single-tenant and multi-tenant VMs:
○ PVS (Provisioning Services) – XenDesktop and XenApp

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Write-cache design with shared storage
Provisioning
Servers
Web Interface VMs Desktop Delivery Controller VMs
Licensing Server
VM
XenApp Server
VMs
XenDesktop
VM Instances
SQL Server VM
Virtual Machines
Active
Directory
Users
Provisioned VMs
HYPERVISOR
SHARED STORAGE

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Write-cache design with local storage
Provisioning
Servers
Web Interface VMs Desktop Delivery Controller VMs
Licensing Server
VM
XenApp Server
VMs
XenDesktop
VM Instances
SQL Server VM
Virtual Machines
Active
Directory
Users
Provisioned VMs
HYPERVISOR
Local write-cache
WRITE-CACHE
SHARED STORAGE

15. micro-POD Design

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A micro-pod is a miniature pod
leveraging local storage
SUM230

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Write-cache on local storage
1,000
500
User Count
Cost, AU100 200
50
User Count
Productivity per user
Within individual server
AU – arbitrary units

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POD
trend
Traditional
trend
Cost-Performance Trends
Shared Storage Local Storage
1,000
500
Combined
Productivity
Cost, AU100 200
1,000
500
Combined
Productivity
100 200 Cost, AU
micro-POD
Performance
trend
micro-POD
trend

19. Building micro-PODs

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Fundamentals of balanced design

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Storage capacity vs. user count
USER_COUNT * VM_DISK + SWAP = TOTAL_DISK
USER_COUNT * (PAGE_FILE + W_CACHE) + SWAP = TOTAL_DISK
PAGE_FILE = VM_RAM * X and SWAP ~ VM_RAM * USER_COUNT
USER_COUNT = TOTAL_DISK ÷ [VM_RAM * (X + 1) + W_CACHE]
VM_DISK SWAPW_CACHEPAGE_FILE
TOTAL_DISK

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Storage capacity vs. user count - Example
Usable Storage capacity* (GiB) User Count
RAID 6 DISKS 8 DISKS 10 DISKS
0 816 1088 1360
5 with HS 544 816 1088
6 544 816 1088
10 408 544 680
50 544 816 1088
RAID 6 DISKS 8 DISKS 10 DISKS
0 116 155 194
5 with HS 77 116 155
6 77 116 155
10 58 77 97
50 77 116 155
* Array with 146Gb drives
USER_COUNT = TOTAL_DISK ÷ [VM_RAM * (X + 1) + W_CACHE]
W_CACHE = 4GB
VM_RAM = 2GB
PAGE_FILE = 1GB, i.e. X = 50%

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Storage performance
RPM IOPS
SSD 5,000+
SAS 15,000 175
SAS 10,000 125
SAS 7,200 75
SAS 5,400 50
IO per Disk
RAID PENALTY
0 1
1 2
5 4
6 6
10 2
50 4
Write Penalties User Workloads
ITEM ~VALUE
IOPS per User 20
Size, KB 4-8
Writes, % 80
Reads, % 20
IOPS = [IOPS per DISK]*[Disk Count]*([% of Reads]+[% of Writes] ÷ [RAID Write Penalty])

24. Are mechanical disks
affordable but just too slow?

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RAID performance for 4K IO workloads
Write coalescing, i.e. “derandomizing” IO in action. 3,000-6,000 IOPS from 6-10 disks
4K IO, Random Write 4K IO, Random Read
Utilization, %
Wait
3,000 IOPS
IOMeter load, XenServer 6.0.2 IOSTAT output, RAID5, 8 SAS-15k disks

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Availability
• For reliability, good performance under failure choose:
○ RAID10
• For RAID with 5 disks or more:
○ RAID6

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Storage cost
TYPE COST, $
SSD 4,000+
SAS 400
Unit Cost
TYPE $ PER MONTH, PER TB
SSD 3,000
SAS 300
Cost of Ownership

28. Quest for an agile well
balanced server

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Modern 1U server
redundant power
high capacity internal storage – 6 to 10 SAS drives
1Gb NICs
Hypervisor management
remote management
space for 10Gb NICs for user and PVS traffic

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Modern 1U server
• 2 socket design, 12-16 cores
• 6-10 15k SAS drives, 146-300Gb each
• Storage grade RAID controllers (0.5-2Gb cache)

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Sufficient capacity and performance
• 0.5-1.5 Tb capacity in RAID 10 (6-10 15k SAS drives, 146Gb or 300Gb)
• 3,000-6,000 IOPs available
• 80-100 concurrent users consume only 1,600-2,000 IOPs at 20 IOPs per user

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Per server hardware cost (including storage)
• $10,000 to $16,000 per server
• Under $200 per user at 80-100 user density per server

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Shared vs. local storage
• High Availability
• Fault Tolerance
• Resource rebalancing
• Maintenance

34. Micro-POD Implementation

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Implementation
Building block:
○ 1 rack
○ 2 PVS Servers
○ 2-4 XenServer pools, ~8-16 servers each
○ Local 10Gb interfaces
○ Utilize PVS subnet affinity
○ Estimated user count ~ 3,000 to 4,000

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3,000-4,000 users per standard rack
HA design with no shared storage
VM hosts with
user workloads
Localized PVS traffic
PVS fail-over traffic
PVS servers
Network switch

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Summary
• Balanced design is key for affordable VDI
• Leverage local storage where possible
• Do not rule out mechanical disks
• Implement modular design for consistent performance and achieve
sustainable growth
• $200 per user in hardware costs is feasible

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References
• http://en.wikipedia.org/wiki/IOPS
• http://en.wikipedia.org/wiki/RAID
• http://en.wikipedia.org/wiki/Point_of_delivery_(networking)

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