Hi

High Availability Design Ram Dantu

Slides are adopted from various sources from Cisco and Interwork Inc.,

Agenda

• Definitions

• Concepts / Calculations

• Examples

• Challenges

Availability as a percentage

1 year = 525960 minutes

Availability Unscheduled downtime per year

99% 3 days 15 hours 36 minutes

99.9% 8 hours 45 min.

99.99% 52 min. 36 sec.

99.999% 5 min. 15 sec.

99.9999% 32 sec.

Getting downtime from availability

1 year = 525,960 minutesUptime = availability * TimeAnnual Uptime = Availability * 525,960Annual Downtime = 525,960 – Annual Uptime---------------------------------------------------------Availability = 0.9999Annual Uptime = .9999 * 525,960Annual Uptime = 525,907.4Annual Downtime = 525,960 – 525,907.4 = 52.596-----------------------------------------------------------Downtime = (1-Availability) * Time

Availability vs. Reliability

Availability = users’ perception

Reliability = individual component failures

Reliability impacts maintenance costs but doesn’t necessarily have to impact availability

Defects Per Million

Availability DPM

99% 10000

99.9% 1000

99.99% 100

99.999% 10

99.9999% 1

Calculating Availability

Availability =MTBF

MTBF + MTTR

Example: 6500 Chassis

MTBF = 369897 hours (about 42 years)

MTTR = 4 hours

Availability = 369897 / ( 369897 + 4 )

= 369897 / 369901

= 0.9999892 = 99.99892%

6500 Availability

Module Availability

Chassis 99.99892%

Power Supplies 99.99873%

Supervisor - including software 99.99516%

GBIC Line Card 99.99577%

GBIC 99.99907%

10/100 Line Card 99.99577%

Availability Formulas

Serial availability

Availability = AvailA × AvailB × AvailC

= 99.999% × 99.999% × 99.999%

= 99.997%

A CB

99.999% 99.999% 99.999%

Availability Formulas

Parallel availability

Availability = 1 – ((1 – AvailA) × (1 – AvailB))

= 1 – ((1 – 99.9%) × (1 – 99.9%))

= 99.9999%

99.9%

99.9%

B

A

Availability Formulas

Parallel-series availability

99.9%

99.9%

B

A

99.9%

99.9%

D

C

99.9%

99.9%

F

E

99.9999% 99.9999% 99.9999%

= 99.9997%

Availability Formulas

Series-parallel availability

99.7%

= 99.9991%

99.9%

99.9%

B

A

99.9%

99.9%

D

C

99.9%

99.9%

F

E

= 1 – ((1 – 99.7%) × (1 – 99.7%))

Core

Distribution

Access

One Core / Distribution 6500

Chassis 99.99892%

Dual power 99.99999%

Supervisor + software 99.99516%

Dual GBIC Line Cards 99.99999%

Dual GBICs 99.99999%

Single switch availability 99.99405%

Pair of Core / Distribution 6500’s

Series-Parallel Availability

99.99405% series availability each

Two switches in parallel

1 – ((1 – 99.99405%) × (1 – 99.99405%))

= 99.999999%

Access Layer 6500

Chassis 99.99892%

Dual power 99.99999%

Dual Supervisors 99.99999%

Dual GBIC Line Cards 99.99999%

Dual GBICs 99.99999%

10/100 Line Card 99.99577%

Switch availability 99.99888%

Access port availability 99.99465%

Challenges

SD

STATUS0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

SD

STAT

US

WS-X6408-GBIC

8 PORTS GIGABIT ETHERNET

1 2 3 4 5 6 7 8

LINK

LINK

LINK

LINK

LINK

LINK

LINK

LINK

SD

STATU

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SUPERVISOR LINK

SYSTEM PORT 2

LINKACTI

VEPW

R MGM

TRESE

T

CONSOLE

SWITCHLOAD1-20%

CONSOLEPORT

1%EJECTPCMCIA

PORT 1

LINK

WS-X6K-SUP1-2GE

SD

STATUS0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

SD

STATU

S

WS-X6408-GBIC

8 PORTS GIGABIT ETHERNET

1 2 3 4 5 6 7 8

LINK

LINK

LINK

LINK

LINK

LINK

LINK

LINK

SD

STATU

S

SUPERVISOR LINK

SYSTE

M PORT 2

LINKACTI

VEPW

R MGM

TRESE

T

CONSOLE

SWITCHLOAD1-20%

CONSOLEPORT

1%EJECTPCMCIA

PORT 1

LINK

WS-X6K-SUP1-2GE

SD

STATU

S0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

SD

STATU

S

WS-X6408-GBIC

8 PORTS GIGABIT ETHERNET

1 2 3 4 5 6 7 8

LINK

LINK

LINK

LINK

LINK

LINK

LINK

LINK

SD

STAT

US

SUPERVISOR LINK

SYSTE

M PORT 2

LINKAC

TIVE

PWR M

GMT

RESET

CONSOLE

SWITCHLOAD1-20%

CONSOLEPORT

1%EJECTPCMCIA

PORT 1

LINK

WS-X6K-SUP1-2GE

• Improving availability at the access layer– “NIC Teaming” in servers– Reduce MTTR

MTBF = 369897 hours

Availability with MTTR of 4 hours = 99.99892%

Availability with MTTR of 2 hours = 99.99945%

Challenges

• Long convergence times– Spanning tree

Eliminate layer-2 links where possible

Avoid layer-2 loops

Use STP enhancements where appropriate– Routing protocols

Use a link-state (or EIGRP) routing protocol

Use routing convergence enhancements

Minimize routing table sizes

Limit convergence scope