IOPS Considerations for VDI Workloads
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  • Let’s go ahead and run through sizing when disk count is known
  • real-word sizing based on host local storage as Tier 1 for VDI workloads.IOPS for VDI workloads is a big deal – a huge deal. Time and time again we this as a primary cause of VDI implementation/user experience issues. Local or shared, VDI workloads significantly affect available IOPS
  • Without actual measures of your workloads, best practices will get you in the neighborhood
  • Current platform as a data point. All IOPS calcs in this deck are based on the represented R/W mix – 70 write/30 read and RAID 10 as that is the local server configuration. Additionally, current and future server density targets defined.

Transcript

  • 1. Sizing for IOPS - Manual Method 1 How do you get this? And this?Citrix documentation says:And provides this:What’s missing? - Number of users - Read/Write Ratio 1
  • 2. Sizing for IOPS - Manual Method 2• Another common IOPS sizing formula is: – Usable IOPS = ((raw IOPS x write%)/write penalty)+ (raw IOPS x read%) - Number of disks to get raw IOPS• What’s missing here? - Read/Write Ratio• 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: Number of disks OR Number of users• If disk count is known, use above formula• If sizing for storage requirements, determine number of users
  • 3. Determine Usable IOPS PowerEdge R720 16 x 146GB 15k SAS – RAID10 Disk IOPS = 175 Write Penalty = 2 30/70 R/W = average and 0/100 R/W = worst case Usable IOPS = ((raw IOPS x write %)/write penalty)+ (raw IOPS x read%) IOPS Disk Write Write Write Read Usable Scenario IOPS Qty Raw IOPS Write % subtotal Penalty IOPS Read % IOPS IOPSAverage 175 16 2800 .7 1960 2 980 .3 840 1820Worst 175 16 2800 1 2800 2 1400 0 0 1400Case The heavy write VDI workload reduces IOPS up to 50% ! 3
  • 4. 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
  • 5. Brining it Together• From real XenDesktop test results: Lifecycle IOPS/desktop Read : Write Steady State 7-8 1% : 99% Boot Storm 16 - 18 13% : 87% Disk Raw Write Write Write Read IOPS Qty IOPS Write % subtotal Penalty IOPS Read % IOPS Usable IOPS 175 16 2800 .99 2722 2 1386 .01 28 1414• 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 Disk Raw Write Write Write Read IOPS Qty IOPS Write % subtotal Penalty IOPS Read % IOPS Usable IOPS 175 16 2800 .87 2436 2 1218 .13 364 1582• 124 users x 18 = 2232 IOPS required in Boot Storm 650 IOPS Short = high latency and slow reboot/user access times 5
  • 6. • 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? We walked through this But what about that?• 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
  • 7. 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
  • 8. 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