Rules of Thumb in Data Engineering

1
Rules of Thumb in Data Engineering

• Jim Gray
• University of Illinois at Urbana Champaign
• 23 April 2001
• Gray_at_Microsoft.com, http//research.Microsoft.com/
  Gray/Talks/

2
Outline

• Moores Law and consequences
• Storage rules of thumb
• Balanced systems rules revisited
• Networking rules of thumb
• Caching rules of thumb

3
Meta-Message Technology Ratios Matter

• Price and Performance change.
• If everything changes in the same way, then
  nothing really changes.
• If some things get much cheaper/faster than
  others, then that is real change.
• Some things are not changing much
• Cost of people
• Speed of light
• And some things are changing a LOT

4
Trends Moores Law

• Performance/Price doubles every 18 months
• 100x per decade
• Progress in next 18 months ALL previous
  progress
• New storage sum of all old storage (ever)
• New processing sum of all old processing.
• E. coli double ever 20 minutes!

15 years ago
5
Trends ops/s/ Had Three Growth Phases

• 1890-1945
• Mechanical
• Relay
• 7-year doubling
• 1945-1985
• Tube, transistor,..
• 2.3 year doubling
• 1985-2000
• Microprocessor
• 1.0 year doubling

6
So a problem

• Suppose you have a ten-year compute job on the
  worlds fastest supercomputer. What should you
  do.
• ? Commit 250M now?
• ? Program for 9 years Software speedup 26
  250x Moores law speedup 26 250x so
  4,000x speedup spend 1M (not 250M on
  hardware) runs in 2 weeks, not 10 years.
• Homework problem What is the optimum strategy?

7
Storage capacity beating Moores law

• 3 k/TB today (raw disk)
• 1k/TB by end of 2002

8
Trends Magnetic Storage Densities

• Amazing progress
• Ratios have changed
• Capacity grows 60/y
• Access speed grows 10x more slowly

9
Trends Density Limits
Density vs Time b/µm2 Gb/in2
Bit Density

• The end is near!
• Products23 GbpsiLab 50 Gbpsilimit
  60 Gbpsi
• Butlimit keeps rising there are alternatives

b/µm2 Gb/in2
? NEMS, Florescent? Holograpic, DNA?
3,000 2,000
1,000 600
300 200
SuperParmagnetic Limit
100 60
30 20
Wavelength Limit
ODD
10 6
DVD
3 2
CD

1 0.6
Figure adapted from Franco Vitaliano, The NEW
new media the growing attraction of nonmagnetic
storage, Data Storage, Feb 2000, pp 21-32,
www.datastorage.com
1990 1992 1994 1996 1998 2000 2002 2004
2006 2008
10
Trends promises NEMS (Nano Electro Mechanical
Systems)(http//www.nanochip.com/) also
Cornell, IBM, CMU,

• 250 Gbpsi by using tunneling electronic
  microscope
• Disk replacement
• Capacity 180 GB now, 1.4 TB in 2 years
• Transfer rate 100 MB/sec RW
• Latency 0.5msec
• Power 23W active, .05W Standby
• 10k/TB now, 2k/TB in 2002

11
Consequence of Moores lawNeed an address bit
every 18 months.

• Moores law gives you 2x more in 18 months.
• RAM
• Today we have 10 MB to 100 GB machines(24-36
  bits of addressing) then
• In 9 years we will need 6 more bits 30-42 bit
  addressing (4TB ram).
• Disks
• Today we have 10 GB to 100 TB file
  systems/DBs(33-47 bit file addresses)
• In 9 years, we will need 6 more bits40-53 bit
  file addresses (100 PB files)

12
Architecture could change this

• 1-level store
• System 48, AS400 has 1-level store.
• Never re-uses an address.
• Needs 96-bit addressing today.
• NUMAs and Clusters
• Willing to buy a 100 M computer?
• Then add 6 more address bits.
• Only 1-level store pushes us beyond 64-bits
• Still, these are logical addresses, 64-bit
  physical will last many years

13
Trends Gilders Law 3x bandwidth/year for 25
more years

• Today
• 40 Gbps per channel (?)
• 12 channels per fiber (wdm) 500 Gbps
• 32 fibers/bundle 16 Tbps/bundle
• In lab 3 Tbps/fiber (400 x WDM)
• In theory 25 Tbps per fiber
• 1 Tbps USA 1996 WAN bisection bandwidth
• Aggregate bandwidth doubles every 8 months!

1 fiber 25 Tbps
14
Outline

• Moores Law and consequences
• Storage rules of thumb
• Balanced systems rules revisited
• Networking rules of thumb
• Caching rules of thumb

15
How much storage do we need?
Yotta Zetta Exa Peta Tera Giga Mega Kilo
Everything! Recorded

• Soon everything can be recorded and indexed
• Most bytes will never be seen by humans.
• Data summarization, trend detection anomaly
  detection are key technologies
• See Mike Lesk How much information is there
  http//www.lesk.com/mlesk/ksg97/ksg.html
• See Lyman Varian
• How much information
• http//www.sims.berkeley.edu/research/projects/how
  -much-info/

All Books MultiMedia
All LoC books (words)
.Movie
A Photo
A Book
24 Yecto, 21 zepto, 18 atto, 15 femto, 12 pico, 9
nano, 6 micro, 3 milli
16
Storage Latency How Far Away is the Data?
Andromeda
9
Tape /Optical
10
2,000 Years
Robot
6
Pluto
Disk
2 Years
10
1.5 hr
Springfield
Memory
100
This Campus
10
10 min
On Board Cache
On Chip Cache
2
This Room
Registers
1
My Head
1 min
17
Storage Hierarchy Speed Capacity vs Cost
Tradeoffs
Price vs Speed
Size vs Speed
Nearline
Cache
Tape
Offline
Main
Tape
Disc
Secondary
Online
Online
Secondary
/MB
Tape
Tape
Disc
Typical System (bytes)
Main
Offline
Nearline
Tape
Tape
Cache
-9
-6
-3
0
3
-9
-6
-3
0
3
10
10
10
10
10
10
10
10
10
10
Access Time (seconds)
Access Time (seconds)
18
Disks Today

• Disk is 8GB to 160 GB10-50 MBps5k-15k rpm
  (6ms-2ms rotational latency)12ms-7ms
  seek2K/IDE-TB, 15k/SCSI-TB
• For shared disks most time spent waiting in queue
  for access to arm/controller

Wait
Transfer
Transfer
Rotate
Rotate
Seek
Seek
19
Standard Storage Metrics

• Capacity
• RAM MB and /MB today at 512MB and 1/MB
• Disk GB and /GB today at 80GB and
  10/GB
• Tape TB and /TB today at 40GB and
  10k/TB (nearline)
• Access time (latency)
• RAM 100 ns
• Disk 15 ms
• Tape 30 second pick, 30 second position
• Transfer rate
• RAM 1-10 GB/s
• Disk 10-50 MB/s - - -Arrays can go to
  10GB/s
• Tape 5-15 MB/s - - - Arrays can go to
  1GB/s

20
New Storage Metrics Kaps, Maps, SCAN

• Kaps How many kilobyte objects served per second
• The file server, transaction processing metric
• This is the OLD metric.
• Maps How many megabyte objects served per sec
• The Multi-Media metric
• SCAN How long to scan all the data
• the data mining and utility metric
• And
• Kaps/, Maps/, TBscan/

21
For the Record (good 1999 devices packaged in
systemhttp//www.tpc.org/results/individual_resul
ts/Compaq/compaq.5500.99050701.es.pdf)
X 100
Tape is 1Tb with 4 DLT readers at 5MBps each.
22
For the Record (good 1999 devices packaged in
systemhttp//www.tpc.org/results/individual_resul
ts/Compaq/compaq.5500.99050701.es.pdf)
Tape is 1Tb with 4 DLT readers at 5MBps each.
23
Disk Changes

• Disks got cheaper 20k -gt 200 (or even 200)
• /Kaps etc improved 100x (Moores law!) (or even
  500x)
• One-time event (went from mainframe prices to PC
  prices)
• Disk data got cooler (10x per decade)
• 1990 disk 1GB and 50Kaps and 5 minute scan
• 2001 disk 160GB and 120Kaps and 1 hour scan
• So
• 1990 1 Kaps per 20 MB
• 2001 1 Kaps per 1,000 MB
• disk scans take longer (10x per decade)
• Backup/restore takes a long time (too long)

24
Storage Ratios Changed

• 10x better access time
• 10x more bandwidth
• 100x more capacity
• Data 25x cooler (1Kaps/20MB vs 1Kaps/500MB)
• 4,000x lower media price
• 20x to 100x lower disk price
• Scan takes 10x longer (3 min vs 45 min)

• RAM/disk media price ratio changed
• 1970-1990 1001
• 1990-1995 101
• 1995-1997 501
• today 6/GB disk 1001
  600/GB ram

25
Data on Disk Can Move to RAM in 10 years
1001
10 years
26
More Kaps and Kaps/ but.

• Disk accesses got much less expensive Better
  disks Cheaper disks!
• But disk arms are expensivethe scarce resource
• 1 hour Scanvs 5 minutes in 1990

27
The Absurd 10x (5 year) Disk

• 2.5 hr scan time (poor sequential access)
• 1 aps / 5 GB (VERY cold data)
• Its a tape!

1 TB
100 MB/s
200 Kaps
28
Disk vs Tape

• Disk
• 80 GB
• 20 MBps
• 5 ms seek time
• 3 ms rotate latency
• 3/GB for drive 3/GB for ctlrs/cabinet
• 15 TB/rack
• 1 hour scan

• Tape
• 40 GB
• 10 MBps
• 10 sec pick time
• 30-120 second seek time
• 2/GB for media8/GB for drivelibrary
• 10 TB/rack
• 1 week scan

Guestimates Cern 200 TB 3480 tapes 2 col
50GB Rack 1 TB 20 drives
The price advantage of tape is narrowing, and
the performance advantage of disk is growing At
10K/TB, disk is competitive with nearline tape.
29
Caveat Tape vendors may innovate

• Sony DTF-2 is 100 GB, 24 MBps 30 second
  pick time
• So, 2x better
• Prices not clear
• http//bpgprod.sel.sony.com/DTF/seismic/dtf2.html

30
Its Hard to Archive a PetabyteIt takes a LONG
time to restore it.

• At 1GBps it takes 12 days!
• Store it in two (or more) places online (on
  disk?). A geo-plex
• Scrub it continuously (look for errors)
• On failure,
• use other copy until failure repaired,
• refresh lost copy from safe copy.
• Can organize the two copies differently
  (e.g. one by time, one by space)

31
How to cool disk data

• Cache data in main memory
• See 5 minute rule later in presentation
• Fewer-larger transfers
• Larger pages (512-gt 8KB -gt 256KB)
• Sequential rather than random access
• Random 8KB IO is 1.5 MBps
• Sequential IO is 30 MBps (201 ratio is growing)
• Raid1 (mirroring) rather than Raid5 (parity).

32
Stripes, Mirrors, Parity (RAID 0,1, 5)

• RAID 0 Stripes
• bandwidth
• RAID 1 Mirrors, Shadows,
• Fault tolerance
• Reads faster, writes 2x slower
• RAID 5 Parity
• Fault tolerance
• Reads faster
• Writes 4x or 6x slower.

0,3,6,..
1,4,7,..
2,5,8,..
0,1,2,..
0,1,2,..
0,2,P2,..
1,P1,4,..
P0,3,5,..
33
RAID 10 (strips of mirrors) Winswastes space,
saves arms

• RAID 5 (6 disks 1 vol)
• Performance
• 675 reads/sec
• 210 writes/sec
• Write
• 4 logical IO,
• 2 seek 1.7 rotate
• SAVES SPACE
• Performance degrades on failure

• RAID1 (6 disks, 3 pairs)
• Performance
• 750 reads/sec
• 300 writes/sec
• Write
• 2 logical IO
• 2 seek 0.7 rotate
• SAVES ARMS
• Performance improves on failure

34
Shows Best Page Index Page Size 16KB
35
Auto Manage Storage

• 1980 rule of thumb
• A DataAdmin per 10GB, SysAdmin per mips
• 2000 rule of thumb
• A DataAdmin per 5TB
• SysAdmin per 100 clones (varies with app).
• Problem
• 5TB is 50k today, 5k in a few years.
• Admin cost gtgt storage cost !!!!
• Challenge
• Automate ALL storage admin tasks

36
Summarizing storage rules of thumb (1)

• Moores law 4x every 3 years 100x more per
  decade
• Implies 2 bit of addressing every 3 years.
• Storage capacities increase 100x/decade
• Storage costs drop 100x per decade
• Storage throughput increases 10x/decade
• Data cools 10x/decade
• Disk page sizes increase 5x per decade.

37
Summarizing storage rules of thumb (2)

• RAMDisk and DiskTape cost ratios are 1001
  and 31
• So, in 10 years, disk data can move to RAM since
  prices decline 100x per decade.
• A person can administer a million dollars of disk
  storage that is 1TB - 100TB today
• Disks are replacing tapes as backup devices.You
  cant backup/restore a Petabyte quicklyso
  geoplex it.
• Mirroring rather than Parity to save disk arms

38
Outline

• Moores Law and consequences
• Storage rules of thumb
• Balanced systems rules revisited
• Networking rules of thumb
• Caching rules of thumb

39
Standard Architecture (today)
40
Amdahls Balance Laws

• parallelism law If a computation has a serial
  part S and a parallel component P, then the
  maximum speedup is (SP)/S.
• balanced system law A system needs a bit of IO
  per second per instruction per secondabout 8
  MIPS per MBps.
• memory law ?1 the MB/MIPS ratio (called alpha
  (?)), in a balanced system is 1.
• IO law Programs do one IO per 50,000
  instructions.

41
Amdahls Laws Valid 35 Years Later?

• Parallelism law is algebra so SURE!
• Balanced system laws?
• Look at tpc results (tpcC, tpcH) at
  http//www.tpc.org/
• Some imagination needed
• Whats an instruction (CPI varies from 1-3)?
• RISC, CISC, VLIW, clocks per instruction,
• Whats an I/O?

42
TPC systems

• Normalize for CPI (clocks per instruction)
• TPC-C has about 7 ins/byte of IO
• TPC-H has 3 ins/byte of IO
• TPC-H needs ½ as many disks, sequential vs random
• Both use 9GB 10 krpm disks (need arms, not bytes)

43
TPC systems Whats alpha (MB/MIPS)?

• Hard to say
• Intel 32 bit addressing ( 4GB limit). Known CPI.
• IBM, HP, Sun have 64 GB limit. Unknown CPI.
• Look at both, guess CPI for IBM, HP, Sun
• Alpha is between 1 and 6

Mips Memory Alpha
Amdahl 1 1 1
tpcC Intel 8x262 2Gips 4GB 2
tpcH Intel 8x458 4Gips 4GB 1
tpcC IBM 24 cpus ? 12 Gips 64GB 6
tpcH HP 32 cpus ? 16 Gips 32 GB 2
44
Instructions per IO?

• We know 8 mips per MBps of IO
• So, 8KB page is 64 K instructions
• And 64KB page is 512 K instructions.
• But, sequential has fewer instructions/byte. (3
  vs 7 in tpcH vs tpcC).
• So, 64KB page is 200 K instructions.

45
Amdahls Balance Laws Revised

• Laws right, just need interpretation
  (imagination?)
• Balanced System Law A system needs 8
  MIPS/MBpsIO, but instruction rate must be
  measured on the workload.
• Sequential workloads have low CPI (clocks per
  instruction),
• random workloads tend to have higher CPI.
• Alpha (the MB/MIPS ratio) is rising from 1 to 6.
  This trend will likely continue.
• One Random IOs per 50k instructions.
• Sequential IOs are larger One sequential IO per
  200k instructions

46
PAP vs RAP

• Peak Advertised Performance vs Real Application
  Performance

47
Outline

• Moores Law and consequences
• Storage rules of thumb
• Balanced systems rules revisited
• Networking rules of thumb
• Caching rules of thumb

48
Standard IO (Infiniband) in 5 Years?

• Probably
• Replace PCI with something better will still
  need a mezzanine bus standard
• Multiple serial links directly from processor
• Fast (10 GBps/link) for a few meters
• System Area Networks (SANS) ubiquitous (VIA
  morphs to Infiniband?)

49
Ubiquitous 10 GBps SANs in 5 years

• 1Gbps Ethernet are reality now.
• Also FiberChannel ,MyriNet, GigaNet, ServerNet,,
  ATM,
• 10 Gbps x4 WDM deployed now (OC192)
• 3 Tbps WDM working in lab
• In 5 years, expect 10x, wow!!

1 GBps
120 MBps (1Gbps)
80 MBps
5 MBps
40 MBps
20 MBps
50
Networking

• WANS are getting faster than LANSG8 OC192
  8Gbps is standard
• Link bandwidth improves 4x per 3 years
• Speed of light (60 ms round trip in US)
• Software stacks have always been the problem.

Time SenderCPU ReceiverCPU bytes/bandwidth
This has been the problem
51
The Promise of SAN/VIA10x in 2 years
http//www.ViArch.org/

• Yesterday
• 10 MBps (100 Mbps Ethernet)
• 20 MBps tcp/ip saturates 2 cpus
• round-trip latency 250 µs
• Now
• Wires are 10x faster Myrinet, Gbps Ethernet,
  ServerNet,
• Fast user-level communication
• tcp/ip 100 MBps 10 cpu
• round-trip latency is 15 us
• 1.6 Gbps demoed on a WAN

52
How much does wire-time cost?/Mbyte?

• Cost Time
• Gbps Ethernet .2µ 10 ms
• 100 Mbps Ethernet .3µ 100 ms
• OC12 (650 Mbps) .003 20 ms
• DSL .0006 25 sec
• POTs .002 200 sec
• Wireless .80 500 sec

53
Data delivery costs 1/GB toady

• Rent for big customers 300/megabit per
  second per month
• Improved 3x in last 6 years (!).
• That translates to 1/GB you send.
• You can mail a 160 GB disk for 20.
• Thats 16x cheaper
• If overnight its 3 MBps.

3x160 GB ½ TB
54
The Network Revolution

• Networking folks are finally streamlining LAN
  case (SAN).
• Offloading protocol to NIC
• ½ power point is 8KB
• Min round trip latency is 50 µs.
• 3k ins .1 ins/byte

• High-Performance Distributed Objects over a
  System Area NetworkLi, L. Forin, A. Hunt, G.
  Wang, Y. , MSR-TR-98-68

55
Outline

• Moores Law and consequences
• Storage rules of thumb
• Balanced systems rules revisited
• Networking rules of thumb
• Caching rules of thumb

56
The Five Minute Rule

• Trade DRAM for Disk Accesses
• Cost of an access (Drive_Cost /
  Access_per_second)
• Cost of a DRAM page ( /MB/ pages_per_MB)
• Break even has two terms
• Technology term and an Economic term
• Grew page size to compensate for changing ratios.
• Now at 5 minutes for random, 10 seconds sequential

57
The 5 Minute Rule Derived

Disk Access Cost /T DiskPrice .
AccessesPerSecond
( )/T
Cost a RAM Page RAM__Per_MB
PagesPerMB

T TimeBetweenReferences to Page

• Breakeven
• RAM__Per_MB _____DiskPrice
  .
• PagesPerMB T x
  AccessesPerSecond

• T DiskPrice x
  PagesPerMB .
• RAM__Per_MB x
  AccessPerSecond

58
Plugging in the Numbers
PPM/aps disk/Ram Break Even
Random 128/120 1 1000/3 300 5 minutes
Sequential 1/30 .03 300 10seconds

• Trend is longer times because disk not
  changing much, RAM declining 100x/decade

5 Minutes 10 second rule
59
The 10 Instruction Rule

• Spend 10 instructions /second to save 1 byte
• Cost of instruction I ProcessorCost/MIPSLi
  feTime
• Cost of byte B RAM__Per_B/LifeTime
• Breakeven NxI B N B/I (RAM__B X
  MIPS)/ ProcessorCost (3E-6x5E8)/500 3
  ins/B for Intel (3E-6x3E8)/10 10 ins/B for
  ARM

60
Trading Storage for Computation

• You can spend 10 bytes of RAM to save 1
  instruction/second.
• Rent for Disk 1/GB (forever)
• Processor costs 10 to 1,000/mips10 - 1,000
  for 100 Tera Ops.
• So 1/TeraOp
• 1 GB 1 Top 1 MB 1 Gop 1 KB 1 Mop
• Save a 1KB object on disk if it costs more than
  10 ms to compute.

61
When to Cache Web Pages.

• Caching saves user time
• Caching saves wire time
• Caching costs storage
• Caching only works sometimes
• New pages are a miss
• Stale pages are a miss

62
Web Page Caching Saves People Time

• Assume people cost 20/hour (or .2 /hr ???)
• Assume 20 hit in browser, 40 in proxy
• Assume 3 second server time
• Caching saves people time 28/year to 150/year
  of people time or .28 cents to 1.5/year.

63
Web Page Caching Saves Resources

• Wire cost is penny (wireless) to 100µ LAN
• Storage is 8 µ/mo
• Breakeven wire cost storage rent 4 to 7
  months
• Add people cost breakeven is 4 years.cheap
  people (.2/hr) ? 6 to 8 months.

64
Caching

• Disk caching
• 5 minute rule for random IO
• 11 second rule for sequential IO
• Web page caching
• If page will be re-referenced in 18 months
  with free users 15 years with valuable
  usersthen cache the page in the client/proxy.
• Challenge guessing which pages will be
  re-referenceddetecting stale pages (page
  velocity)

65
Meta-Message Technology Ratios Matter

• Price and Performance change.
• If everything changes in the same way, then
  nothing really changes.
• If some things get much cheaper/faster than
  others, then that is real change.
• Some things are not changing much
• Cost of people
• Speed of light
• And some things are changing a LOT

66
Outline

• Moores Law and consequences
• Storage rules of thumb
• Balanced systems rules revisited
• Networking rules of thumb
• Caching rules of thumb