Supermicro SuperChassis 745TQ-R920B manuale d’uso

SC745TQ-R1200B SC745TQ-920B SC745TQ-R800(B) SC745S2-R800(B) SC745TQ-800(B) SC745S2-800(B) USER’S MANUAL 1.0a SC745 CHASSIS Series S UPER ®[...]

SC745 Chassis Manual ii Manual Revision 1.0a Release Date: December 1, 2010 The information in thi s U ser’s Manual has been carefully re viewed and is believed to be accurate. The vendor assumes no responsibi lity for any inaccura cies that may be co ntained in this docum ent, makes no commitment to update or to keep current the information in t[...]

iii Preface Preface About This Manual This man ual is written for prof essional system integrators and PC technicians. It provides information for the installation and use of the SC745 4U chassis. Installa - tion and mainten ance should be performed by expe rienced technicians only . Supermicro's SC745 chassis series is optimized for the lates[...]

SC745 Chassis Manual iv Manual Organization Chapter 1: Introduction The rs t chapter pr ovides a chec klist of the main compone nts included with this chassis and describ es the m ain features of the SC745 chass is. This chapt er also includes contact information. Chapter 2: System Safety This chapter list s warnings, precautions, and sys tem sa[...]

v Preface Appendix A: Chassis Cables Appendix B: Power Supply Specications Appendix C: SAS-743TQ Backplane Manual[...]

SC745 Chassis Manual vi T able of Contents Chapter 1 Introductio n 1-1 Overview ............................................................................................ 1- 1 1-2 Chassis Models ................................................................................. 1- 1 1-3 Chassis Features .............................................[...]

vii Preface Chapter 5 Chassis Setup and Maintenanc e 5-1 Overview ............................................................................................ 5- 1 5-2 Installation Procedures ...................................................................... 5- 1 General Maintenance ..............................................................[...]

SC745 Chassis Manual viii Appendix A SC745 Chassis Cable s Appendix B SC745 Power Supply Specication s Appendix C SAS-743TQ Backplane Specication s[...]

Chapter 1 Introduction 1-1 Overview Supermicro’s SC745 4U chassis fe atures a u nique and highly-o ptimized design. The chassis is equipped with high efciency power supply . High-performance fans provide ample optimized cool ing for FB-DIMM memory modules and eight hot-swappable drive bays of fer maximum storage capacity in a 4U form factor . [...]

SC745 Chassis Manual 1-2 1-3 Chassis Features The SC745 4U high-performance chassis includes the following features: CPU The SC745 ch assis supports a DP/UP (dual p rocessor/single proce ssor). Please refer to the motherboard specications pages on our W eb site for updates on sup - ported processors. Hard Drives The S C745 chassis features e igh[...]

1-3 Chapter 1: Introduction 1-4 Contacting Supermicro Headquarters Address: Super Micro Computer , Inc. 980 Rock Ave. San Jose, CA 95131 U.S.A. T el: +1 (408) 503-8000 Fax: +1 (408) 503-8008 Email: marketing@supermicro.com (General Information) support@supermicro.com (T echnical Support) Web Site: www .supermicro.com Europe Address: Super Micro Com[...]

SC745 Chassis Manual 1-4 Notes[...]

Chapter 2: System Safety 2-1 Chapter 2 System Safety 2-1 Overview This c hapter provides a quick setup checkli st to get your chassis up and running. Following the steps in th e order given should enable you t o h ave your chassis set up and operational within a minimal amount of time. This quick setup assumes that you are an experienced technician[...]

SC745 Chassis Manual 2-2 2-4 Electrical Safety Precautions Basic electr ical safety precaution s should be followed to protect yourself from harm and the SC745 from damage: Be aware of the lo cations of the power on/off switc h on th e chass is as w ell • as the ro om’ s emerge ncy power-off switch, disconnec tion switch or electrica l outle[...]

Chapter 2: System Safety 2-3 Handle used batteries carefully . Do not damage the battery in any way , a dam - • aged bat tery may releas e haz ardous materials into th e env ironment. Do no t discard a used battery in the garbage or a public landll. Please comply with the regulations set up by y our loca l hazard ous wast e manage ment age [...]

SC745 Chassis Manual 2-4 Use a grounded wrist strap designed to prevent electrostatic discharge. • Keep al l components and printed circuit boards (PCBs) in their antistat ic bags • until ready for use. T ouch a g rounded metal o bject before rem oving any board from its an tistatic • bag. Do not let components or PCBs come into cont[...]

3-1 Chapter 3: Chassis Components Chapter 3 Chassis Components 3-1 Overview This chapter describes the most common components included with your chassis. Some components listed may not be included or compatible with your particular chassis model. For mo re informa tion, see the installation instructions detailed later in this manual. 3-2 Components[...]

SC745 Chassis Manual 3-2 Fans The SC745 chassis accepts three system fans and two rear exhaust fans. System fans for SC745 chassis are powered from the serverboar d. These fans are 4U high and are powered by 4 -pin connectors. Mounting Rails (optional) The SC745 can be place d in a rack for secure storage and u se. T o setup you r rack, follow the [...]

4-1 Chapter 4: System Interface Chapter 4 System Interface 4-1 Overview There are several LEDs on the control panel as well as others on the drive carriers to keep you constantly informed of the overall status of the system, as well as the activity and health of specic components. Most SC745 models have two buttons on the control panel, a reset [...]

Chassis Manual 4-2 4-2 Control Panel Buttons There are two push-buttons located on the front of the chassis. These are the power on/off button and the reset button. Power: • The main power switch is u sed to a pply or r emove power from the power supply to the server system. T urning off the system power with this but - ton removes the main po[...]

4-3 Chapter 4: System Interface NIC2: • Indicates network activity on GLAN2 when ashing. NIC1: • Indicates network activity on GLAN1 when ashing. HDD: • Indicates IDE channel activity . SAS/SA T A drive, SCSI drive, and/or DVD- ROM drive activity when ashing. Power: • Indicates power is being supp lied to the system&apo[...]

Chassis Manual 4-4 4-4 Drive Carrier LEDs Y our chassi s uses SAS/SA T A or S CSI drives, but not both. SAS/SA T A Drives Each SAS/SA T A drive carrier has two LEDs. Green: • Eac h SAS/SA T A dr ive c arr ier h as a gre en LED. Wh en ill uminat ed, th is gre en L ED (on t he f ront of t he SAS/SA T A d rive car ri er) ind icat es dr ive acti v[...]

5-1 Chapter 5: Chassis Setup and Maintenance Chapter 5 Chassis Setup and Maintenance 5-1 Overview This chapter covers the steps required to install components and perform mainte - nance on the chassis. The only tool you will need to install components and perform maintenance is a Phillip s screwdrive r . Print this page to use as a re ference whil [...]

SC745 Chassis Manual 5-2 5-3 Removing the Chassis Front and Side Covers Figure 5-1: Removing the Chassis Cover Side Cover The Side Cover Removing the Chassis Side Cover Push the cover latch button to release the latch handle. 1. Pull the cover off the chass is using the latch handle. 2. Replacing the Chassis Side Cover With the latch handle open sl[...]

5-3 Chapter 5: Chassis Setup and Maintenance The Front Cover The front cover ho uses up to eight hot-swappable hard drives. The cover can be locked to preven t unauthor ized acce ss. The key to this lock is shi pped with th e system. Removing the Front Cover Unlock the front cover using the key shipped with the system. 1. Pull the cover open using [...]

SC745 Chassis Manual 5-4 5-4 Conguring the Storage Module Storage Module T ower or Rack Conguration The SC745 cha ssis is sh ipped in tower mod e and can be immedi ately us ed as desktop serve r . If th e c hassis is to be used in a rack, y ou must turn the storage module ninety degrees. This can be done before, during, or after setup. Figure[...]

5-5 Chapter 5: Chassis Setup and Maintenance Rotating the Storage Module for Rack Mounting Open the chassis cover . 1. Locate the storage module and disconnect any cables from the storage mod - 2. ule to any component in the chassis. Push the storage module release lever. This lever unlocks the storage mod - 3. ule. Grasp the extern al edges of the[...]

SC745 Chassis Manual 5-6 Adding Drives to the Storage Module The storage module includes three full-sized drive bays and the front LED panel. The storage module can be set up one of three ways: A. Add up to three e xtra hard drives to the drive tray s. B. Add up to three peripheral drives (CD-ROM, DVD-ROM, etc.) drive trays. C. Add ve hot swappa[...]

5-7 Chapter 5: Chassis Setup and Maintenance Drive T ray Release T abs Adding up to Three Peripheral/Hard Drives to the Drive T rays Open the chassis cover . 1. Locate the drive t ray release tab for the slot you wan t t o place the peripheral 2. drive. Push the drive tray toward the front of the chassis. 3. Figure 5-7: Remove Drive T ray[...]

SC745 Chassis Manual 5-8 Place the hard dri ve into the hard drive tray . Make sure the t ype of hard drive 4. (SAS/SA T A or SCSI ) i s supported by the motherboar d. The hard d rive may not completely ll the tray . Secure the hard drive to the tray with four screws from the bottom. 5. Slide the hard drive into the chassis until the tray clicks[...]

5-9 Chapter 5: Chassis Setup and Maintenance Drive T ray Release T abs Up to three peripheral drives (DVD-ROM, CD-ROM and others) may be added to the drive trays . Adding up to Three Peripheral Drives to the Drive Trays Open the chassis cover . 1. Locate the drive t ray release tab for the slot you wan t t o place the peripheral 2. drive. Push the [...]

SC745 Chassis Manual 5-10 Remove the hard dr ive tray rails from the hard drive t ray . T o do th is, you must 4. remove two screws from each side. Attach the rail s t o a DVD-ROM, CD-ROM or other perip herals. Th e rails 5. should t any standard sized peripherals. Slide the peripheral into the chassis until the tray clicks into place. 6. Repeat[...]

5-1 1 Chapter 5: Chassis Setup and Maintenance Drive T ray Release T abs The SC74 5 chassis accep ts an M35TQ or M35S (SCSI) mobile rack to install extr a hot-swappable hard drives. The mobile rack goes into the storage module which goes into the chassis. For more information on mobile racks, visit the Supermicro Web site at www. supermicro.com. Ad[...]

SC745 Chassis Manual 5-12 Mobile Rack Hard Drive Rails Remove the hard dr ive tray rails from the hard drive t ray . T o do th is, you must 4. remove two screws from each side. Do this for all three hard drive trays. Attach the rail s t o a DVD-ROM, CD-ROM or other perip heral. T he rails should 5. t any standard sized peripherals. Hard Drive Ra[...]

5-13 Chapter 5: Chassis Setup and Maintenance The drives are mounted in drive carriers to simplify their installation and removal from the chass is. These carrier s also help promote pr oper air ow for the dr ive bays. Installing Hard Drives to the Chassis Unlock and open the chassis cover. 1. Press the release button to extend the drive tray ha[...]

SC745 Chassis Manual 5-14 Figure 5-15: Remove Dummy Drive Tray Secure the hard drive to the tray using four screws. 6. Insert the hard drive into the chassis using the following steps: 7. 7a. Press the hard drive release button to extend the drive tray handle. 7b. Insert the hard drive into the chassis and close the handle to lock the hard drive in[...]

5-15 Chapter 5: Chassis Setup and Maintenance I/O Shield 5-6 Installing the Motherboard I/O Shield The I/O shield hold s t he motherboard ports in place. Ins tall the I/O shield before you install the motherboard. Figure 5-17: SC745 Chassis I/O Shield Installing the I/O Shield: Review the docu mentation that came with your mot herboard. Become fami[...]

SC745 Chassis Manual 5-16 Permanent and Optional Standoffs Standoffs prevent short circuits by securing space between the motherboard and the chassis surface. The SC745 chassis packaging includes optio nal standoffs (hexagonal-shaped posts). These standoffs accept the rounded Phillips head screws which are also included in the SC745 accessories pac[...]

5-17 Chapter 5: Chassis Setup and Maintenance Installing the Motherboard Motherboard Installation Review the docu mentation that came with your mot herboard. Become familiar 1. with component placement, requirements, and precautions. Disconnect the power supply and lay the chassis on a at surface. 2. Open the chassis cover . 3. As required by yo[...]

SC745 Chassis Manual 5-18 Power Supply Connections Connect each o f the foll owing cables as required by your m otherboard manufacture r . In some instances not all of these cables are require d, and some cables may not be included with the motherboard. Power Supply Cable Name No. Connects to Description 20-pin or 24-pin power cable 1 motherboard 2[...]

5-19 Chapter 5: Chassis Setup and Maintenance Expansion Card and PCI Slot Setup After the motherboard has been installed, expansion cards may be installed. Installing Expansion Cards Locate the release tab on the top of the PCI slot bracket. 1. Gently apply pressure in the middle of the release tab to unlock the PCI slot 2. bracket. Pull the releas[...]

SC745 Chassis Manual 5-20 Remove the scre w h olding the bracket in place and pu ll the bracket from the 4. chassis. Install your PCI card or other add-on card into the PCI slot bracket and moth - 5. erboard. T o do this, slide the PCI card (with "L" bracket) into the PCI slot and secure the card to the motherboard. Push the PCI brack et [...]

5-21 Chapter 5: Chassis Setup and Maintenance 5-7 Installing the Air Shroud Figure 5-21: Air Shroud Air shroud s concentrate airo w to maximize fan efciency . The SC 745 chassis air shroud does not require screws to set up. NOTE: The air shroud includes tabs that can be removed if motherboard compo - nents prevent the air shroud from tting[...]

SC745 Chassis Manual 5-22 Figure 5-22: Air Shroud in Place Checking the Airow Make sure there ar e no objects to obstruct airow in a nd out of the server . In 1. addition, if you a re using a front bezel, make sure th e b ezel's lter is replaced periodically . Do not operate the s erver without drives or drive tr ays in the drive bays[...]

5-23 Chapter 5: Chassis Setup and Maintenance Five heavy-duty fans provide cooling for the chassis. Three fans are located in the front of the chassis with two fans in the rear . These fans circulate air thr ough the chassis as a means of lowering the internal temperature of the chassis. The fans come pre-installed to the chassis. Each fan is hot-s[...]

SC745 Chassis Manual 5-24 Rear Fan Release T ab Figure 5-24: Rear Chassis Fans Replacing a Rear Chassis Fan Press the rear fan release tab. 1. Pull the fan from the chassis top rst. 2. Place the new fan in the chassis bottom rst. 3. Push the fan fully into the housing until the fan clicks into place. 4.[...]

5-25 Chapter 5: Chassis Setup and Maintenance Depending on your chassis model, the SC745 chassis has an 800, 920 or 1200 W att power supply . "R" model chassis feature a second redundant power supply . This power supply is auto-switching capable. This enables it to automatically sense and operat e at a 100v to 240v input voltage . An ambe[...]

SC745 Chassis Manual 5-26 Notes[...]

6-1 Chapter 6: Rack Installation Chapter 6 Rack Installation 6-1 Overview This c hapter provides a quick setup checkli st to get your chassis up and running. Following these steps in the order given should enable you to have the system operational within a minimum amount of time. 6-2 Unpacking the System Y ou should inspect the box the chassis was [...]

SC745 Chassis Manual 6-2 Rack Precautions Ensure that the leveling jacks on the bottom of the rack are fully extended to • the oor with the full weight of the rack resting on them. In single rack installation, stabilizers should be attached to the rack. • In multiple rack installations, the racks should be coupled together . • Alw[...]

6-3 Chapter 6: Rack Installation Rack Mounting Considerations Ambient Operating T emperature If installed in a closed or multi-unit rack assembly , the ambient operating tempera - ture of the rack environme nt may b e greater than the ambient tem perature of the room. Therefore, consideration should be given to installing the equipment in an enviro[...]

SC745 Chassis Manual 6-4 6-4 Rack Mounting Instructions This section provides information on insta lling the SC745 chassis into a rack unit with the rails provided. There are a variety of rack units on the market, which may mean the assembly procedure will differ slightly . Y ou should also refer to the instal - lation instructions that came with t[...]

6-5 Chapter 6: Rack Installation Removing the T op Cover Locate the chassis cover lock (blue lever) at the rear of the chassis cover . 1. Slide the chassis cover lock to the right and push chassis cover forward. 2. Lift the chassis top cover off the chassis. 3. Removing the Chassis Feet Place the chassis on its side with the chassis side cover faci[...]

SC745 Chassis Manual 6-6 Figure 6-2: Identifying the Inner Rails and Chassis Handles Chassis Handle Inner Rails Chassis Handle Screw Chassis Rail Screw Identifying the Sections of the Rack Rails The cha ssis package includes two rack rail a ssemblies in the rack mounting kit. Each as sembly consists of two sections: an inner xed chassis rail th [...]

6-7 Chapter 6: Rack Installation Figure 6-3: Ins talling the Inner Rack Rails Installing the Chassis Handles and Inner Rails Locate the two chassis handles and six handle screws. 1. Align the chass is handle with the front of the chassi s and secure with the 2. three chassis handle screws. Repeats steps 1 and 2 with the other handle. 3. Locate the [...]

SC745 Chassis Manual 6-8 Installing th e Outer Rails onto the Rack Attach the fron t a nd rear short brackets to the outs ide of the long bracket. 1. Both bracket ends must face the same direction. Adjust both the brackets to the proper distance so that the rail ts snugly into 2. the rack. Secure the front s ide of the outer rail with two M5 scr[...]

6-9 Chapter 6: Rack Installation Figure 6-5: Installing the Chassis into a Rack Installing the Chassis into a Rack Conrm that chas sis includes the inner rails and t he outer rails. 1. Line chassis rails with the front of the rack rails. 2. Slide the chass is rails into the rack rails, keepi ng the pressure even on both 3. sides (it may be nec e[...]

SC745 Chassis Manual 6-10 6-5 T ower Mounting Instructions The SC745 chassis is shipp ed with the chass is cover and fee t pre-installed. T o use the chassis as a desktop server, no other installation is required. Use the instructions in this section if you have converted the chassis for rack use and need to return the chassis to tower mounting. In[...]

6-1 1 Chapter 6: Rack Installation Placing the Chassis Feet Place the chassi s foot in the foot receptacle and sl ide the foot toward the 1. front of the chassis. The foot should lock into place. Secure the foot to the chassis using one screw enclosed in the packaging. 2. Repeat steps 1 and 2 for the remaining three chassis feet. 3. Chassis Foot Re[...]

SC745 Chassis Manual 6-12 Notes[...]

A-1 Appendix A: Chassis Cables Appendix A SC745 Chassis Cables A-1 Overview This appendix list s supported cables f or your chassis syste m. It o nly includes the most commonly used components and congurations. For more compatible cables, refer to the manufacturer of the motherboard you are using and our Web sit e at: www .supermicro.com. A-2 Ca[...]

SC745 Chassis Manual A-2 A-4 Compatible Cables The following c ables are compatible with the SC7 45 chassis. Some compatible mo therboards hav e d if fe rent connectors . If your m otherboard has on ly one SAS connector th at the SAS/ SA T A cables m ust share, use one of the following cables. These cables must be purchased separately . Description[...]

A-3 Appendix A: Chassis Cables Extending Power Cables Although Supermicro chassis are designed with to be efcient and cost-ef fective, some compatible motherboards have power connectors located in different areas. T o use th ese mot herboards you m ay have to extend the power cables to the mother boards. T o do this, use the following chart as a[...]

SC745 Chassis Manual A-4 Notes[...]

B-1 Appendix B: Power Supply Specications Appendix B SC745 Power Supply Specications This appendix lists power supply specications for your chassis system. 800W (Redundant = X2) MFR Part # PWS-801-1R Rated AC V oltage 100 - 240V 50 - 60Hz 10 - 4 Amp +5V standby 4 Amp +12V 66 Amp +5V 30 Amp +3.3V 24 Amp -12V 0.6 Amp 920W (Redundant = X2 MFR[...]

SC745 Chassis Manual B-2 1200W (Redundant = X2) MFR Part # PWS-1K21P-1R Rated AC V oltage 100 - 140V , 50 - 60Hz, 8 - 1 1.5 Amp 180 - 240V , 50 - 60Hz, 5.5 - 8 Amp DC Output +12V 1000W , 83 Amp @ 100-140V 1200W , 100 Amp @ 180-240V 5Vsb: 4A DC Output with PDB +5V : 50 Amp +3.3V : 30 Amp -12V : 0.6 Amp[...]

C-1 Appendix C: SAS-743TQ Backplane Specications Appendix C SAS-743TQ Backplane Specications T o avoid personal injury and property damage, carefully follow all the safety steps listed below when accessing your system or handling the components. C-1 ESD Safety Guidelines Electrostatic Discharge (ESD) can damage electronic com ponents. T o pre[...]

C-2 SC745 Chassis Manual C-3 An Important Note to Users All images an d layouts shown in this user's guide a re based upon the latest PCB • revision available at t he time of p ublishing. The card you have received may or may not look exactly the same as the graphics shown in this manual. C-4 Introduction to the SAS-743TQ Backplane The SA[...]

C-3 Appendix C: SAS-743TQ Backplane Specications +12V +12V GND GND GND GND +5V +5V 48 1 16 64 49 H12 H7 H4 M71 M75 M86 M87 H5 H6 H3 M90 M91 M96 M97 MM2 MM3 SAS743TQ REV 3.00 R S UPER pb C-5 Front Connectors, Jumpers and LEDs JT AG Connector: JP47 1. Upgrade Connector: JP46 2. Chip: MG9072 3. Power Connectors (4-pin): JP10, 4. and JP13 ACT IN: JP[...]

C-4 SC745 Chassis Manual C-6 Front Connector and Pin Denitions #5. Activity LED Header The activity LED header , designated JP26, is u sed to ind icat e th e ac tiv ity st atu s of each SAS drive. The Activity LED Header is located on the front panel. For the Activity LED He ader to wor k pro perly , connect using a 10-pin LED cable. #3. MG9072 [...]

C-5 Appendix C: SAS-743TQ Backplane Specications #6. and #7. Sideband Headers The sideband headers ar e d esignated JP51 and JP52. For SES-2 to work properly , you must connect an 10-pin sideband cable. See the table to the right for pin deni - tions. Sideband Headers Pin # Denition Pin # Denition 2 Backplane Addressing (SB5) 1 Controll[...]

C-6 SC745 Chassis Manual C-7 Front Jumper Locations and Pin Denitions +12V +12V GND GND GND GND +5V +5V 48 1 16 64 49 H12 H7 H4 M71 M75 M86 M87 H5 H6 H3 M90 M91 M96 M97 MM2 MM3 SAS743TQ REV 3.00 R S UPER pb +12V +12V GND GND GND GND +5V +5V 48 1 16 64 49 H12 H7 H4 M71 M75 M86 M87 H5 H6 H3 M90 M91 M96 M97 MM2 MM3 SAS743TQ REV 3.00 R S UPER pb JP5[...]

C-7 Appendix C: SAS-743TQ Backplane Specications Explanation of Jumpers T o modify the operation of the backplane, jumpers can be u sed t o ch oose between opt ional se tting s. Ju mpers cr eate shor ts between two pins to change the funct ion of the connector . Pin 1 is identied with a square sol der pad on the printed c ircuit board. Note: [...]

C-8 SC745 Chassis Manual I 2 C and SGPIO Mode Jumper Settings This backplane can utilize I 2 C or SGPIO. I 2 C is the default mode and can be used without making cha nges to your jumpers. The following informatio n de tails which jumpers must be congured to use SGPIO mode or restore your backplane to I 2 C mode. I 2 C and SGPIO Settings Jumper I[...]

C-9 Appendix C: SAS-743TQ Backplane Specications Front Panel LEDs LED State Specication D3 ON Overheat/drive failure LED indicator (Red light: ashing, Buzzer: On, if activated) Front LED Indicators +12V +12V GND GND GND GND +5V +5V 48 1 16 64 49 H12 H7 H4 M71 M75 M86 M87 H5 H6 H3 M90 M91 M96 M97 MM2 MM3 SAS743TQ REV 3.00 R S UPER pb OH/Dri[...]

C-10 SC745 Chassis Manual C-8 Rear Connectors and LED Indicators Rear SAS/SA T A Connectors Rear Connector SAS Drive Number SAS #0 SAS/SA T A HHD #0 SAS #1 SAS/SA T A HHD #1 SAS #2 SAS/SA T A HHD #2 SAS #3 SAS/SA T A HHD #3 SAS #4 SAS/SA T A HHD #4 SAS #5 SAS/SA T A HHD #5 SAS #6 SAS/SA T A HHD #6 SAS #7 SAS/SA T A HHD #7 Rear LED Indicators Rear L[...]

C-1 1 Appendix C: SAS-743TQ Backplane Specications Notes[...]

C-12 SC745 Chassis Manual Disclaimer (cont.) The products sold by Supermicro are not intended for and will not be used in life sup- port systems, medical equipment, nuclear facilities or systems, aircraft, aircraft devices, aircraft/emergency communication devices or other critical systems whose failure to per - form be reasonably expected to resul[...]