Dell Compellent Storage Center SAN & Citrix XenDesktop 1,000 Desktop Reference Architecture. Dell Compellent Technical Solutions

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1 Dell Cmpellent Strage Center SAN & Citrix XenDesktp 1,000 Desktp Reference Architecture Dell Cmpellent Technical Slutins

2 THIS REFERANCE ARCHITECTURE IS FOR INFORMATIONAL PURPOSES ONLY, AND MAY CONTAIN TYPOGRAPHICAL ERRORS AND TECHNICAL INACCURACIES. THE CONTENT IS PROVIDED AS IS, WITHOUT EXPRESS OR IMPLIED WARRANTIES OF ANY KIND Dell Inc. All rights reserved. Reprductin f this material in any manner whatsever withut the express written permissin f Dell Inc. is strictly frbidden. Fr mre infrmatin, cntact Dell. Dell, the DELL lg, and the DELL badge and Cmpellent are trademarks f Dell Inc. Citrix, XenServer and XenDesktp are trademarks f Citrix Systems Inc. Micrsft and Hyper-V are trademarks f Micrsft Crp. Other trademarks and trade names may be used in this dcument t refer t either the entities claiming the marks and names r their prducts. Dell Inc. disclaims any prprietary interest in trademarks and trade names ther than its wn. August

3 Cntents Figures... 4 Intrductin... 5 Executive Summary... 5 Key Findings... 6 Tested Architecture... 6 Fast Track... 8 Lad Generatin... 8 System Center Virtual Machine Manager... 9 XenDesktp Windws Antivirus...10 Strage Center Cnfiguratin...10 XenDesktp Master Image Management...10 Machine Create Service and Hyper-V Cnfiguratin...11 Data Prgressin and Replay technlgy and the Master Image...12 Testing Results...14 Bt Test...14 Lad Test...16 Medium Wrklad Results...17 Heavy Wrklad Results...18 Dynamic Memry Cnsideratin...19 Functinal IOPS...20 Cnclusin...21 Reference Materials

4 Figures Figure 1. Tested Architecture... 8 Figure 2. Virtual Disk Relatinship per Vlume... 9 Figure 3. Strage Tiers Figure 4. Custm Strage Prfile Figure 5. CSV Tiers Figure 6. Replay Statistics Figure 7. SSD IOPS During Bt Strm Figure 8. 15K IOPS During Bt Strm Figure 9. IOPS with Medium Wrklad Figure 10. KBPS with Medium Wrklad Figure 11. IOPS with Heavy Wrklad Figure 12. KBPS with Heavy Wrklad

5 Intrductin The intentin f this dcument is t prvide technical prfessinals with infrmatin t assist in the planning, design and deplyment f a Dell Cmpellent Strage Center SAN in a Citrix XenDesktp VDI envirnment using Micrsft Hyper-V 2008 R2 as the hypervisr. This dcument is based n internal testing f 1,000 virtual desktps n 12 physical servers. The data fr this dcument was gathered and validated at the Dell Cmpellent lab and design center. This dcument fcuses n the impact f a virtual desktp infrastructure (VDI) n the Dell Cmpellent Strage Center SAN. As such, detailed infrmatin n hst, netwrk and ther supprting infrastructure is ut f the scpe f this dcument. Hst, netwrk and supprting infrastructure is imprtant t a VDI deplyment and shuld als be carefully evaluated when planning a VDI prject. The infrmatin in this dcument is t serve as a reference t implementing VDI with the Dell Cmpellent Strage Center SAN. Wrklads will be different fr each rganizatin, depending n applicatins and infrastructure. As such, it is strngly recmmended that each rganizatin run a VDI pilt t gather sizing and IOPS data as a basis fr purchasing and prvisining the crrect amunt f strage. Executive summary Prper strage cnfiguratin is imprtant t the success f a VDI prject. A Dell Fluid Data architecture and Dell Cmpellent integrated sftware features, such as autmated tiered strage, thin prvisining, cntinuus snapshts and remte replicatin, prvide a highly effective strage ptin fr Citrix XenDesktp and Hyper-V. Dell Cmpellent Dynamic Capacity sftware separates strage allcatin frm utilizatin. While administratrs can create strage vlumes f any size fr virtualized applicatins, physical capacity is cnsumed nly when data is written t the disk. With thin prvisining, IT grups can avid purchasing excess capacity upfrnt. When applicatins require mre strage, the system prvisins it frm the pl f unused capacity. Fr instance, thin prvisining can present 10 virtual strage vlumes, 1TB each, fr use by 10 unique servers, but nly require the physical capacity that is actually written fr each hst. In additin, autmated tiered strage frm Dell Cmpellent, called Data Prgressin, can help rganizatins ptimize the use f strage in a Citrix XenServer envirnment with Micrsft Hyper-V. Data Prgressin can statically r dynamically mve blcks f data between tiers f strage based n perfrmance characteristics. This allws the intelligent use f all tiers f strage, withut the write penalty typically assciated with traditinal strage arrays. Utilizing Data Prgressin, all writes int the strage array ccur at Tier 1, RAID 10. Over time, the sftware dynamically mves thse blcks t mre efficient RAID levels, and the less frequently accessed blcks t lwer tiers f strage. Data Prgressin reduces the need fr large numbers f high-perfrmance, high-cst disks by mving frequently used data t higher perfrmance tiers f strage while mving infrequently used data t lwer cst, higher-density disks. The migratin f data is dne n the blck level, s data within a vlume can be mved based n perfrmance characteristics. These technlgies help t create an efficient strage platfrm fr Citrix XenDesktp with Micrsft Hyper-V. 5

6 Key findings The Dell Cmpellent Technical Slutins team tested a sample f 1,000 virtual desktps and simulated real-wrld wrklads using Citrix XenDesktp with Micrsft Hyper-V. The envirnment included a Dell Cmpellent Strage Center SAN, 10GB iscsi cnnectivity and a Lgin Cnsultants Lgin VSI scripted lad-generatin slutin. Lgin VSI uses standard ffice applicatins with peridic wait times t generate the wrklad f a typical knwledge wrker. Tw lad tests were perfrmed, ne with a medium wrklad and ne with a heavy wrklad emulating 1,000 pwer users. During the deplyment f XenDesktp virtual desktps, an instance f the template VM is cpied t the vlume where the virtual desktps will reside. This is a shared, read-nly cpy f the template that new virtual machine differencing and identity infrmatin will reference. Using Dell Cmpellent Data Instant Replay and Data Prgressin, this read-nly prtin f the vlume was mved t the SSD tier f strage while the read-write virtual machine differencing and identity infrmatin stayed n the 15K tier f strage. Using a medium wrklad generated a peak f 6,800+ ttal IPOS and 125,000+ KBPS, while the heavy wrklad generated a peak f 7,500+ IOPS and 160,000+ KBPS. During the medium test, average read IOPS were 37 percent and write IOPS were 63 percent. The heavy wrklad generated 33 percent read and 67 percent write IOPS n average. In additin t the lad test, a bt strm was emulated by pwering n 1,000 virtual desktps simultaneusly. This generated IOPS as high as 40,000 with a data rate f ver 700 MBPS. During the bt strm an average f 70 percent f IOPS came frm the SSD tier f strage, while the remaining 30 percent came frm the 15K disk tier. The length f the bt strm while measuring sustained high IOPS was six minutes. Tested architecture The tested envirnment was cmprised f 12 Hyper-V servers running Windws Server 2008 R2 Enterprise editin in tw clusters with six ndes per cluster. Each cluster was assigned six, 2TB Cluster Shared Vlume (CSV) vlumes fr hsting the virtual desktps. Six CSVs were created t increase the number f cmmand queues Micrsft Windws has t access the virtual hard disks (VHDs). The disk size f 2TB was beynd the requirement fr the test. Hwever, with thin prvisining little space was wasted n the SAN. An additinal seven virtual hst servers were used t supprt the tested envirnment. This included tw servers fr infrastructure tasks, such as Active Directry, SQL Server, System Center Virtual Machine Manager (SCVMM) and XenDesktp. The remaining five were used fr lad generatin. Fllwing are the specifics n the hardware used. 12 Windws Server 2008 R2 Enterprise servers as virtual hsts fr tested envirnment Dual Quad Cre Intel Xen X GHz prcessr 72GB RAM Dual-prt Intel 10GbE NIC, Mdel x520-da2 fr netwrk and iscsi Micrsft sftware iscsi initiatr 6

7 All recent updates and ht fix KB Windws Server 2008 R2 Enterprise servers as virtual hsts fr infrastructure Dual Quad Cre Intel Xen X GHz prcessr 72GB RAM Dual-prt Intel 10GbE NIC, Mdel x520-da2 fr netwrk and iscsi Virtualized infrastructure including: 2, AD Dmain cntrllers 1, SCVMM server 1, XenDesktp 5 server 1, Dell Cmpellent Enterprise Manager Data Cllectr server 1, Windws Server 2008 R2 file server 1, SQL Server 2008 server 5 Windws Server 2008 R2 Enterprise servers as virtual hsts fr lad generatin Dual Quad Cre Intel Xen X GHz prcessr 32GB RAM Dual Bradcm 1GB NIC 5 virtual servers per hst used fr lad generatin 2 Dell Cmpellent Strage Center SAN Series 40 cntrllers 48, 2.5-inch 146GB 15K SAS drives 3, 2.5-inch 200GB SSD SAS drives Firmware Versin GB iscsi Dell Cmpellent Fast Track-enabled 7

8 Figure 1. Tested Architecture Fast Track The desktp deplyment utilized the Dell Cmpellent Strage Center SAN feature Fast Track, which dynamically places the mst frequently used data n the fastest, r uter, tracks f each drive. By cntinually ptimizing data placement n each disk, Fast Track eliminates wasted space n the fastest prtin f the drive. In this test, Fast Track was used n every drive within the system. Lad Generatin T accurately represent a real-wrld scenari, a lad generatin utility was used thrughut the test. The lad was generated using Lgin Cnsultants Lgin VSI applicatin. One test was run with a lad set t medium and a secnd with a setting t heavy. With Lgin VSI, the tests replicated a wrklad f all 1,000 virtual desktps lgging in and used a variety f ffice applicatins such as Micrsft Outlk, Office and Internet Explrer, as well as PDF creatin and Flash mvies. 8

9 System Center Virtual Machine Manager System Center Virtual Machine Manager 2010 R2 (SCVMM) was used t manage the hsts and all virtual desktps. SCVMM als prvides the interface frm XenDesktp and Machine Creatin services t deply and manage desktps within the clusters. XenDesktp 5 T prepare fr the desktp deplyment, a single virtual machine (VM) was created n an infrastructure server as the base image fr XenDesktp. This image was cnfigured with Windws 7 SP1, Micrsft Office and ther business applicatins. The Virtual XenDesktp Desktp Agent was installed fr management within XenDesktp. Lastly, the Lgin VSI Target installer was initiated t prepare the image fr the Lgin VSI Lad Generatin. Once the base image was ready, it was clned t each cluster using SCVMM. Clning the base image t each cluster makes it available t XenDesktp t use as a master image. Machine Creatin Services cpied this master image t each vlume n the cluster when the new machine catalg was created. XenDesktp then used the master disk and a unique identity and differencing disk t create each VM. The cnfiguratin t deply the virtual desktps is as fllws: Desktps created with Machine Creatin Services Machine type pled, randmly assigned Tw hst grups, ne fr each cluster Tw catalgs f 500 virtual desktps, ne fr each cluster One desktp grup with all 1,000 virtual desktps Figure 2. Virtual Disk Relatinship per Vlume 9

10 Windws 7 The virtual desktps platfrm fr all tests was Windws 7 Prfessinal 32-bit. Each VM was cnfigured with ne vcpu and 768MB f memry. The Windws page file was set t twice the size f available RAM. Micrsft Office 2007 was installed, as well as the applicatins required fr Lgin VSI. The template desktp was ptimized using the Citrix XenCnvert Optimizer applicatin. Antivirus N antivirus prduct was utilized within the VMs. Intrducing traditinal antivirus sftware may dramatically increase the I/O lad f the VM. Special cnsideratin shuld be taken when implementing antivirus prgrams in a virtual envirnment. Using virtualizatin-aware antivirus applicatins may reduce the I/O requirements within the virtual envirnment. Strage Center Cnfiguratin The Dell Cmpellent Strage Center SAN was designed t maximize perfrmance in a VDI envirnment. A pl f disks was created with tw tiers f strage within the SAN. The first tier cnsisted f three 200GB SSDs, and the secnd tier cnsisted f frty-eight 146GB SAS drives. Strage Center was running firmware versin during the test. Figure 3. Strage Tiers A custm strage prfile was created t accmmdate the perfrmance characteristics f the tw drive types used in testing. The strage prfile definitin allwed writes t cme in at RAID 10 n Tier 2, while allwing Replay (snapsht) data t migrate up t the Tier 1 SSD level. (Fr details n creating custm strage prfiles, see the Dell Cmpellent Administratin Guide). XenDesktp Master Image Management One bjective f the testing was t split read-nly data that is shared between all virtual desktps frm the read-write data that is unique t each virtual desktp. By splitting this data, the Dell Cmpellent Strage Center SAN can better utilize the perfrmance characteristics f bth the SSD and 10

11 SAS drives within the system. Master image management allws read-nly data t reside n the SSD tier, while read-write transactins take place n the 15K SAS tier f strage. Figure 4. Custm Strage Prfile Machine Create Service and Hyper-V Cnfiguratin Virtual desktps were created using XenDesktp Machine Creatin Services (MCS) n Hyper-V 2008 R2 with Cluster Shared Vlumes (CSV). As mentined previusly, MCS cpies the master r base image nt each CSV during virtual desktp creatin. MCS then creates a differencing and identity disk that each VM uses t stre unique data. The master image is a read-nly cpy f the virtual desktp template used in cnjunctin with the differencing and identity disk t create the cmplete virtual desktp image. (See Figure 2). The space that the VMs cnsume must be cnsidered with the cnfiguratin used during testing because f the affect it has n the SSD tier f strage. After initial deplyment f the virtual desktps and befre they are pwered n, the differencing and identity data cnsume apprximately 16MB f data. With a base image f 8.4GB and the differencing and identity infrmatin frm 82 t 84 virtual desktps n each CSV, the ttal amunt f space cnsumed n a CSV befre any virtual desktps are turned n is apprximately 10GB. With 12 CSVs in the testing infrastructure, ttal space cnsumed befre the virtual desktps were started was apprximately 120GB. Once the virtual desktps are pwered n and users have lgged in, the differencing and identity data will grw. In ur testing, the space used by the differencing and identity data after a Lgin VSI lad test was apprximately 2.2GB. Ttal amunt f space used n a CSV after the lad test was apprximately 185GB. The ttal space cnsumed fr all CSVs was 2.3TB. * All drive space figures are apprximate and will change depending n the envirnment. Fr best results, use a pilt prgram t determine drive space needs within yur envirnment. 11

12 Data Prgressin, Replay Technlgy and the Master Image Natively with XenDesktp MCS, it is nt pssible t split the read-nly and read-write data n a vlume basis. This is because the shared master image is stred with the identity and differencing data n each vlume. Hwever, in the tested infrastructure, Dell Cmpellent Replay technlgy and Data Prgressin were used t vercme this and mve the read-nly master image data t SSDs while directing all virtual desktp specific read-writes t the 15K SAS drives. The steps invlved t split the master image reads frm virtual desktp specific read-writes were: Create disk pls and strage prfile as utlined abve. Create new vlumes, attach them t the cluster and cnfigure as CSV. Create the virtual desktps in XenDesktp, placing the virtual desktps n the new CSVs. D nt pwer n the virtual machines. Run cnfiguratin scripts t set VLAN r startup cnfiguratin. Create a Manual Replay set t Never Expire n the new CSVs. Cntinue cnfiguratin specific t yur envirnment, starting the virtual desktps as necessary. Fllwing the steps abve, the disk pls and strage prfile were cnfigured as utlined in the Strage Center Cnfiguratin sectin. This set all writes t cme in as RAID 10 n Tier 2, while mving Replay data t RAID 5 n Tier 1. Next, new CSVs fr the virtual desktps were created. (It is imprtant t create a new vlume t guarantee that n data resides n the vlumes. When finalized, the new vlumes shuld be mapped and cnfigured as CSVs n the hypervisr). The virtual desktps were then deplyed using XenDesktp. As nted abve, at the pint where the desktps have been deplyed but befre they are pwered n, they cnsume a limited amunt f data. In the test envirnment, this included 8.4GB fr the master image and 16MB f space fr differencing and identity infrmatin per virtual desktp. This data is primarily read-nly and will be lcked using Dell Cmpellent Replay technlgy and migrated t the SSD tier using Data Prgressin. Any cnfiguratin scripts, such as setting VLAN tagging r mdifying pwer-n settings, can be run at this pint, prviding they dn t pwer n the virtual desktps. Als, be cautius f assigning the virtual desktps t a desktp pl, as XenDesktp may pwer n the virtual desktp autmatically. After the virtual desktps are deplyed, a manual Replay set t Never Expire is created n the vlumes. This will lck all blcks n the vlume and allw them t migrate t Tier 1 when Data Prgressin runs. By lcking these blcks befre the virtual desktps are pwered n, the read-nly data (the master image) can be split frm the read-write data (differencing and identity). The small amunt f identity and differencing data lcked in the Replay will nt have an effect n perfrmance f the virtual desktps. Figure 5 illustrates hw the data resides n each tier f strage within a vlume. 12

13 Figure 5. CSV Tiers Figure 6 shws ne f the CSV vlumes used fr testing. Within this vlume, 9.2GB f data was mved t Tier 1 n the SSD drives cnfigured as RAID 5. The rest f the data resided n the lwer tier as RAID 10 with Fast Track (the uter 20 percent f the disk) r RAID 10 standard. Ttal data n the vlume, nt including RAID verhead, was 111GB. Figure 6. Replay Statistics Using Dell Cmpellent Replay and Data Prgressin technlgy, each vlume is divided in a way that allws read-intensive data (in this case, the master image) t reside n the SSD tier, while read-write (differencing and identity) data stays n the SAS tier. This leads t cst savings because the SSDs are nly required fr read-intensive data within the vlume. With this cnfiguratin there is n need t 13

14 size SSDs fr the entire VDI infrastructure, nly the prtin f the data that will benefit frm the high read IOPS f the SSDs. Testing Results Testing fr this reference architecture invlves measuring tw perfrmance indicatrs. The first indicatr is the amunt f IOPS cnsumed during a bt strm. The secnd indicatr measures the perfrmance f all 1,000 desktps during simulated user lad. Bt test The bt test represents a wrst-case scenari where all 1,000 virtual desktps are pwered n simultaneusly. This situatin wuld nt take place during nrmal XenDesktp peratin due t XenDesktp s pwer management functinality. Hwever, it is plausible that many desktps will need t be started quickly in a prductin envirnment, pssibly when recvering frm an utage. A bt strm als prvides a gd measurement f verall back-end strage perfrmance. In ur testing, the length f the bt strm was measured by examining the duratin f sustained high IOPS during a simultaneus pwer n f all 1,000 virtual desktps. In the cnfiguratin utlined abve, with the master image residing n SSDs, and all ther read-write peratin cming in n SAS drives, the average length f the bt strm was six minutes. During the bt strm, ttal IOPS ranged frm 35,500 t 39,500. Seventy percent f all IOPS came frm the read-nly SSD tier, while the remaining 30 percent came frm the 15K SAS tier. Read latency n the 15K SAS tier spiked t 9ms with an average f 4.5ms. Write latency averaged 6ms during the same time. There was n measurable read latency n the SSD tier f strage. The graphs belw shw an example f ne f the bt tests perfrmed with 1,000 virtual desktps. As the graphs shw, the majrity f reads came frm SSDs during the bt. This is due t the OS data n the master image residing n Tier 1. There is als an initial read spike n the 15K SSD tier with the number f writes increasing as the systems are bted. After the bt strm, the number f writes surpasses the number f reads. 14

15 Figure 7. SSD IOPS During Bt Strm 15

16 Figure 8. 15K IOPS During Bt Strm Lad Test The gal f the lad test is t identify the impact f the lad n the Dell Cmpellent SAN. Tw lad tests were perfrmed against the 1,000 desktps using Lgin Cnsultants Lgin VSI Pr. One test was cnducted with the lad set t medium with flash, and ne ran with a lad set t heavy. (Fr details, see the Lgin Cnsultants Wiki.) Medium Wrklad with Flash Emulates a knwledge wrker using Office, Internet Explrer and a PDF Sessins repeat every 12 minutes Respnse time measured every 2 minutes Opens 5 applicatins simultaneusly Type rate is set t 160ms fr each character Apprximately 2 minutes f idle time included t simulate real-wrld users Heavy Wrklad Based n medium wrklad Mre memry and CPU-intensive Simulates a pwer user 16

17 Type rate is 130ms per character Idle time is nly 40 secnds Opens 8 applicatins simultaneusly With bth the medium and heavy wrklads the Lgin VSI applicatin was cnfigured t run in parallel mde. Parallel mde evenly distributes the sessins acrss all the Lgin VSI clients that generate the lgin activity. The test was set t launch client lgns ver 10,000 secnds. In this cnfiguratin the Lgin VSI client launched ne remte cnnectin every 10 secnds. The test cntinued t run fr ne hur after the last sessin lgged in, creating a sustained wrklad f 1,000 sessins fr ne hur. Medium Wrklad Results This test was run with Lgin VSI set t a medium wrklad with flash enabled. The average IOPS fr the entire test was 4,817. This includes the virtual desktp lgin and the hur f sustained wrklad. The average f the 12 highest data pints representing the mst active hur f testing was 6,088 IOPS. The average IOPS during the last hur f testing when all virtual desktps were lgged in and running was 5,363. The chart belw shws the read, write and ttal IOPS during the duratin f the medium wrklad test. The first prting f the test leading up t the highest data pint represents the lgin f the 1,000 virtual desktps. The remaining prtin f the chart shws the final hur f sustained wrklad. Figure 9. IOPS with Medium Wrklad IOPS with Medium Wrklad Read IOPS Write IOPS Ttal IOPS The next chart shws the data thrughput during the test represented by kilbits per secnd. As with the previus chart, the data leading up t the highest data pint represents the VM lgin f ne virtual desktp every 10 secnds. The remaining prtin represents the final hur f sustained wrklad. During the last hur f the test with all machines lgged in and the lad running, 16 percent f all IOPS were read and the remaining 84 percent were write. Figure 10. KBPS with Medium Wrklad 17

18 KBPS with Medium Wrklad Read KBPS Write KBPS Ttal KBPS Heavy Wrklad Results Running a heavy wrklad created an average IOPS f 5,281 during the duratin f the test. This includes the virtual desktp lgin and the hur f sustained wrklad. The average f the highest 12 data pints during the test was 6,652. The average IOPS prduced during the last hur f testing, the pint after virtual desktp lgin while all sessins were running, was 6,118. The chart belw shws the read, write and ttal IOPS during the heavy wrklad test. The first prtin f the test leading up t the highest data pint represents the lgin f the 1,000 VMs. The remaining part f the chart shws the hur f sustained wrklad. Figure 11. IOPS with Heavy Wrklad 8000 IOPS with Heavy Wrklad Read IOPS Write IOPS Ttal IOPS 18

19 The next chart shws the data thrughput during the test represented by kilbit per secnd. As with the previus chart, the data leading up t the highest data pint represents the VM lgin f ne virtual desktp every 10 secnds. The remaining prtin represents the final hur f sustained wrklad. During the last hur f testing while all machines were lgged in and the lad running, 19 percent f the IOPS were read while the remaining 83 percent were write. Figure 12. KBPS with Heavy Wrklad KBPS with Heavy Wrklad Read KBPS Write KBPS Ttal KBPS Dynamic Memry Cnsideratin When XenDesktp creates virtual desktps in Hyper-V, memry is set t a static amunt. This ties the number f virtual desktps t the amunt f RAM n the hst despite actual memry requirements. Dynamic Memry can imprve virtual desktp density by assigning RAM t each guest accrding t its need. Based n dcuments published by Dell and Micrsft, it is pssible t increase density up t 40 percent per server using Dynamic Memry. The tests in this dcument were cnducted with memry statically set t 768MB n each virtual desktp. Each hst had a ttal f 72GB f RAM. The ttal amunt f available RAM n the hst was 3GB with all 84 virtual desktps started. With 3GB f free space it wuld have been pssible t add three mre desktps n each hst, leaving sme rm fr additinal hst verhead. This wuld have resulted in a ttal f 88 virtual desktps per hst, r a ttal f 1,056 desktps ver the 12 hsts. T increase the density in the test envirnment, Dynamic Memry was enabled n all 1,000 virtual desktps. Starting RAM was set t 384MB, and maximum usable memry was set t 1GB. All virtual desktps were pwered n, and Lgin VSI was used t place the virtual desktps under a medium wrklad. During the medium wrklad, the amunt f assigned memry ranged frm 512MB t 670MB. The average amunt f RAM used by the hst was 56GB, r 80 percent f available RAM. The hsts had apprximately 14.5GB f RAM available with Dynamic Memry enabled when placed under a medium lad. Estimating memry usage t be 600MB average under a lad and leaving sme space fr additinal verhead, an additinal 24 virtual desktps were added per hst. This brught the ttal number f desktps per the 12 hsts t 1,296. This cnfiguratin allwed fr the running f 240 mre desktps than with static memry, a 23 percent gain ver the number f virtual desktps supprted using static memry. 19

20 Functinal IOPS Functinal IOPS are imprtant with VDI due t the high write requirement f virtual desktps. Sme estimates put the number f writes in a VDI envirnment up t 90 percent f all IOPS. This can affect the number f IOPS available due t the write penalties assciated with different RAID types. Write penalties are assigned t RAID levels based n characteristics f their write activity. Fr example, with RAID 1 r 10, data is written nce and read nce t verify each write. This cnsumes tw raw IOPS, s RAID 1 and 10 are assigned a write penalty f tw. Likewise, RAID 5 with 4 drives has a penalty f 4 because each write peratin requires fur raw IOPS, ne t read the existing data, ne t read existing parity, ne t write new data, and ne t write new parity. The write penalty increases with the number f drives in the RAID set. T calculate functinal IOPS, the number f raw IOPS are factred with the percent f reads and writes alng with the RAID penalty. The frmula fr calculating functinal IOPS is expressed as: Functinal IOPS=((Raw Strage IOPS*Write %)/RAID Write Penalty)+(Raw Strage IOPS*Read %) In the example belw, fur 146GB 15K drives in a RAID 5 cnfiguratin with 80% write t 20% read rati will prvide 288 functinal IOPS. Functinal IOPS=((720*80%)/4)+(720*20%) In cmparisn, if the abve were changed t RAID 10 instead f RAID 5, the functinal IOPS wuld be 648. Functinal IOPS=((720*80%)/2)+(720*20%) Fr mre infrmatin n functinal IOPS in a XenDesktp envirnment, see the Dell Cmpellent dcument Functinal IOPS in VDI with Dell Cmpellent. 20

21 Cnclusin Based n the test results, the strage requirements fr 1,000 desktps shuld be built t supprt 7,000 IOPS. Hwever, t accurately size a strage system the percent f write IOPS and the RAID penalty fr thse writes must be factred in. Adjusting fr RAID penalty will give the functinal IOPS required when prvisining data strage. During the tw lad tests, an average f 30 percent f the IOPS were read, while the remaining 70 percent were write. With the cnfiguratin utlined in this dcument, all write IOPS ccur at RAID 10. This is the default fr all writes n a Dell Cmpellent Strage Center SAN. RAID 10 has a RAID penalty f tw, meaning it takes tw raw IOPS t perfrm a single write. Factring the RAID penalty in the calculatin belw, we can cnclude that it will take 11,900 raw IOPS t supprt 1,000 desktps. Functinal IOPS = ((7000*70%)*2)+(7000*30%) T meet the read-write requirements using 15K SAS drives, the test team estimates IOPS per drive t be 250. Given 250 IOPS per 15K SAS drive, it wuld take 48 drives t supprt a 1,000 user envirnment during nrmal peratin. In sme envirnments, there may be a requirement t supprt aggressive bt strms, such as what may be experienced at the beginning f the wrkday while users lg in. In ur tests, the IOPS requirement increases up t 40,000 during a bt strm with the majrity f IOPS being read. At 250 IOPS, it wuld take K drives t supprt this number f IOPS during a bt strm. The testing team was able t reduce the number f drives t supprt a bt strm by placing the master image nt SSDs during the tests. The number f drives can be determined by space requirements, as the SSDs can handle nearly 30,000 read IOPS. Latency is als an imprtant cnsideratin in a VDI envirnment. During the lad tests, there was n measurable read latency n the SSD drives. The baseline write latency fr the 15K disk pl was 7ms, and the read latency baseline was 5ms fr the same pl f disks. The preceding tests used XenDesktp with Pled-Randm desktps. These desktps are nt persistent and typically rely n Citrix Prfile Management r ther prfile management strategy t deliver userspecific data t the desktp. As such, we did nt factr in space requirements fr user data in ur testing. Hwever, this shuld be cnsidered when implementing a VDI envirnment. 21

22 Reference Materials The Dell Cmpellent Administratin Guide is available n the Dell Cmpellent Custmer Prtal Citrix Dell Micrsft Dynamic Memry Slutin Overview Virtualizatin-Density-fr-Custmers-by-40-Percent-with-New-Sftware/ Desktp Virtualizatin Tp 10 Mistakes %20Tp%2010%20Mistakes%20Identified%20When%20Ding%20Desktp%20Virtualizatin.pdf Hyper-V Netwrk Cnnectivity ht fix Lgin Cnsultants Lgin Cnsultants WIKI Windws 7 Optimizatin Functinal IOPS in VDI with Dell Cmpellent 22