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Sizing for IOPS - Manual Method 1

Citrix documentation says:

And provides this:

What’s missing?

How do you get this?And this?

- Number of users- Read/Write Ratio

Sizing for IOPS - Manual Method 2

• Another common IOPS sizing formula is:– Usable IOPS = ((raw IOPS x write%)/write penalty)+ (raw IOPS x read%)

• What’s missing here?

• Read/Write Ratio is needed in both cases– Without actual numbers, best practice for R/W:

• 30/70 R/W = average• 0/100 R/W = worst case

• Still required:• If disk count is known, use above formula• If sizing for storage requirements, determine number of users

- Number of disks to get raw IOPS- Read/Write Ratio

Number of disks OR Number of users

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Determine Usable IOPS

PowerEdge R720

16 x 146GB 15k SAS – RAID10

Write Penalty = 2

Disk IOPS = 175

IOPS Scenario

Disk IOPS Qty Raw IOPS Write %

Write subtotal

Write Penalty

Write IOPS Read %

Read IOPS

Usable IOPS

Average 175 16 2800 .7 1960 2 980 .3 840 1820Worst Case 175 16 2800 1 2800 2 1400 0 0 1400

Usable IOPS = ((raw IOPS x write %)/write penalty)+ (raw IOPS x read%)

The heavy write VDI workload reduces IOPS up to 50% !

30/70 R/W = average and 0/100 R/W = worst case

Determine Users per Usable IOPS• How many users can I support?

– Available IOPS Range = 1400-1820– Required variable – IOPS/User

• Citrix XenDesktop Workload Standards

• Average: 1820 / 10 = 182 users • Worst Case: 1400 /10 = 140 users

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Brining it Together

Disk IOPS Qty

Raw IOPS Write %

Write subtotal

Write Penalty

Write IOPS Read %

Read IOPS Usable IOPS

175 16 2800 .99 2722 2 1386 .01 28 1414

Lifecycle IOPS/desktop Read : WriteSteady State 7 - 8 1% : 99%

Boot Storm 16 - 18 13% : 87%

• From real XenDesktop test results:

• Results: 1414 / 8 = 176 users (theoretical at 100%)• Results at 70% IOPS consumption = 124 users• Let’s look at the Boot Storm scenario, requiring recalculation

• 124 users x 18 = 2232 IOPS required in Boot Storm

Disk IOPS Qty

Raw IOPS Write %

Write subtotal

Write Penalty

Write IOPS Read %

Read IOPS Usable IOPS

175 16 2800 .87 2436 2 1218 .13 364 1582

650 IOPS Short = high latency and slow reboot/user access times

Know your Workloads• As I opened with, sizing storage for VDI workloads is complex• Using Best Practice numbers provide a guideline only• Where on this chart do your users fall in?

• Using our scenario of 1414 IOPS and Heavy Windows 7 users– At 70% utilization – 1414 x .7 = 990 / 50 = 20 users / server

• Conversely, if you have 500 users, to determine IOPS– 500 x 50 = 25,000 IOPS + 30% headroom = 32,500 IOPS required

We walked through this

But what about that?

Shared Storage Sizing

• Sizing Shared Storage for Capacity – Straight forward and easy, no tricks or gotchas– Only caveat is knowing the RAID implications OR– Use published Usable Capacity numbers

• Sizing Shared Storage for IOPS – different story– Everything discussed applies– What we cannot account for is vendor implementations

• Controller features and capabilities• “Secret Sauce”• Hybrid disk configurations / algorithms

• We conduct an incredible amount of testing and validation to provide the information to make informed decisions.– Login VSI to generate workload– Liquidware Labs Stratusphere to measure user experience

Recommendations

• Use a performance tool to define IOPS for each Use Case– Perfmon works for Windows – Liquidware Labs Stratusphere– Lakeside Software Systrack

• Once IOPS requirement established multiply by Users• Add at least 30% headroom for storms, growth, etc.• Determine functional requirements

– Are the virtual desktops stateless? (persistent vs. non-persistent)– Do you require live migration, high-availability…– Ultimately determine whether local host storage is appropriate

• If host local is specified, use the enclosed methods

• If shared storage is specified, require your vendor of choice or partner to provide storage specifications