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The Four Horsemen of
Storage System Performance
Stephen Foskett
stephen@fosketts.net
@SFoskett
Blog.Fosketts.net
© Foskett...
Stephen Foskett
is the organizer of Tech Field Day,
proprietor of Gestalt IT,
strangely interested in storage,
baseball be...
© Foskett Services 3
The Rule of Spindles
© Foskett Services 4
The Nature of Disks
• Disks are mechanical – heat,
vibration, rotation, seek
• Read/write heads can only
access a single s...
Combining Spindles
• Spread data across drives to
overcome disk performance
limits
• RAID was invented for this
© Foskett ...
The Rule of Spindles
• Adding more spindles is
usually faster than adding
faster spindles
• Disks just can’t get much
fast...
Never Enough Cache
© Foskett Services 8
Overcoming the Limits of Spindles
• Solid state storage is much
faster than disks – RAM, flash,
etc
• Most modern storage ...
Five Uses for Disk Buffers
• Read cache - frequently-requested data is read
from memory rather than disk
• I/O-matching - ...
Write-Through and Write-Back Cache
© Foskett Services 11
I/O As a Chain of Bottlenecks
© Foskett Services 12
The Chain of Command
• Storage isn’t just disks and
arrays; all that data has to go
somewhere
• Most I/O travels through f...
The Bottle Neck
• How long will it take to fill or
empty a disk drive or array?
• Which is the slowest link?
• Can we brin...
A Chain of Bottlenecks
© Foskett Services 15
A Lack of Intelligence
© Foskett Services 16
The Stack of Lies
• We have lots of compute
power, but very little
communication through the I/O
stack
• Each layer simpli...
De-Multiplex and Communicate
• Generally, more
communication through the
stack gives a better result
overall
• Removing th...
Building Better Storage
© Foskett Services 19
Defeating the Four Horsemen
1. Understand the nature of
disks
2. Tier storage
3. Attack bottlenecks
4. Get integrated
© Fo...
Thank You!
Stephen Foskett
stephen@fosketts.net
@SFoskett
blog.fosketts.net
TechFieldDay.com
21
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The Four Horsemen of Storage System Performance

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Why do some data storage solutions perform better than others? What tradeoffs are made for economy and how do they affect the system as a whole? These questions can be puzzling, but there are core truths that are difficult to avoid. Mechanical disk drives can only move a certain amount of data. RAM caching can improve performance, but only until it runs out. I/O channels can be overwhelmed with data. And above all, a system must be smart to maximize the potential of these components. These are the four horsemen of storage system performance, and they cannot be denied.

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The Four Horsemen of Storage System Performance

  1. 1. The Four Horsemen of Storage System Performance Stephen Foskett stephen@fosketts.net @SFoskett Blog.Fosketts.net © Foskett Services 1
  2. 2. Stephen Foskett is the organizer of Tech Field Day, proprietor of Gestalt IT, strangely interested in storage, baseball believer, all-around nerd, car nut, Microsoft MVP and VMware vExpert, former first-chair bass clarinet player and punk rock frontman, obsessive about lightbulbs, lover of a good Manhattan, watch blogger, Apple blogger, vegetarian blogger, dad to three kids with anagram names, grammar obsessive, avid reader, King of the Andals and the First Men, humanist, frequent traveler, and (apparently) lover of his own voice © Foskett Services 2
  3. 3. © Foskett Services 3
  4. 4. The Rule of Spindles © Foskett Services 4
  5. 5. The Nature of Disks • Disks are mechanical – heat, vibration, rotation, seek • Read/write heads can only access a single spot on the disk at once • Sequential throughput is much higher than random © Foskett Services 5
  6. 6. Combining Spindles • Spread data across drives to overcome disk performance limits • RAID was invented for this © Foskett Services 6
  7. 7. The Rule of Spindles • Adding more spindles is usually faster than adding faster spindles • Disks just can’t get much faster • Slower disks are becoming the norm © Foskett Services 7
  8. 8. Never Enough Cache © Foskett Services 8
  9. 9. Overcoming the Limits of Spindles • Solid state storage is much faster than disks – RAM, flash, etc • Most modern storage systems are tiered, with RAM, flash, and disk • Solid-state is more expensive, but flash is getting cheaper all the time © Foskett Services 9
  10. 10. Five Uses for Disk Buffers • Read cache - frequently-requested data is read from memory rather than disk • I/O-matching - slower disks and faster interfaces work together • Read-around (ahead or behind) pre-fetch cache • Read-after-write - saving recently-written data to serve later read requests • Command queue – writes are reordered © Foskett Services 10
  11. 11. Write-Through and Write-Back Cache © Foskett Services 11
  12. 12. I/O As a Chain of Bottlenecks © Foskett Services 12
  13. 13. The Chain of Command • Storage isn’t just disks and arrays; all that data has to go somewhere • Most I/O travels through five or more busses or channels between CPU and disk drive © Foskett Services 13
  14. 14. The Bottle Neck • How long will it take to fill or empty a disk drive or array? • Which is the slowest link? • Can we bring storage closer to compute? © Foskett Services 14
  15. 15. A Chain of Bottlenecks © Foskett Services 15
  16. 16. A Lack of Intelligence © Foskett Services 16
  17. 17. The Stack of Lies • We have lots of compute power, but very little communication through the I/O stack • Each layer simplifies for the next • Disks “know” nothing about data (and neither do most arrays) © Foskett Services 17
  18. 18. De-Multiplex and Communicate • Generally, more communication through the stack gives a better result overall • Removing the I/O blender will help © Foskett Services 18
  19. 19. Building Better Storage © Foskett Services 19
  20. 20. Defeating the Four Horsemen 1. Understand the nature of disks 2. Tier storage 3. Attack bottlenecks 4. Get integrated © Foskett Services 20
  21. 21. Thank You! Stephen Foskett stephen@fosketts.net @SFoskett blog.fosketts.net TechFieldDay.com 21

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