Joe Wach

1
Joe Wach

• Large Sectors
• Seagate Technology

2
Drive to Reliability Larger sector advantage

• The Disc Drive industry has been challenged to
  increase the reliability of HDDs.
• ECC capability increases have allowed for
  continued increase in disc capacities
• Increasing ECC however, reduces format
  efficiency, which in turn requires an increase in
  areal density this cycle has reached a limit of
  minimal to no payback.
• To break this cycle the industry has long
  discussed increasing sector sizes to allow
  increased ECC capability and improved format
  efficiency.
• Both of which provide additional margin to the
  drive design

3
Sector Sizes Historical Perspective

• 40MB Drive 80,000 Sectors
• Sector Resolution on order of 1/100,000th or
  .00001 or .001
• Today 400GB Drive 800,000,000 Sectors
• Sector Resolution on order of 1/1,000,000,000 or
  .000000001 or .0000001
• Fine resolution is good when managing small
  amounts
• One could argue that with increased capacity,
  resolution of access need not increase
• If sector size grew and number of sectors held
  constant (holding resolution constant) today's
  sectors would be 5MB each!

4
Historical Areal Density Enablers

• Little to No Host Visibility
• Magneto Resistive Head
• PRML Channel
• Closed Loop Servo (Digital)
• Digital Filter
• ECC
• Adaptive Fly Height
• Perpendicular
• Negative Pressure Heads
• Some Visibility
• Zone Based Recording
• Variable Bit Aspect Ratio

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512B Emulation

• Reads - Writes
• Defect Management
• Long Operations

Buffer
Interface
Read / Write
RD/WR Channel
ATA Interface
ECC
Servo
Host
Formatter /Sequencer
Buffer Manager
Data Manager
SATA
Sector 512B
Servo
Sector 512B
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Alignment
1KB
Disc Sectors
Even Length - Aligned
512B
Host Sectors
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What is LBA Alignment? - 1K Sector Example
Host 4
Host 1
Host 3
Host 5
Host 0
Host 2
Even Alignment
Disk 0
Disk 1
Disk 2
Host 4
Host 1
Host 3
Host 0
Host 2
Odd Alignment
Disk 0
Disk 1
Disk 2
Windows XP Natural Odd Alignment
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Read
Drive Data Buffer
512B Host Request
1K Disc Sector
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Write
Target Disc Sector
Drive Data Buffer
512B Host Data
512B Host Data
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Summary 1K Sector Performance (vs 512B Sector)

• Performance
• Windows XP (PCMark 04 Overall)
• Aligned Parity
• Not Aligned -16 to 24
• RAID 0 Aligned 12
• RAID 0 Misaligned 25
• IOMeter (XP)
• Random Reads Parity
• Sequential Reads Parity
• Random Writes 37
• Sequential Writes Parity
• Linux (Bonnie)
• SATA and PATA Aligned Parity
• SATA and PATA Misaligned 30 to 50

Parity /- 5
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Seagate Timeline
Pilot units complete customer integration process
Ship units to pilot partners
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Partition Alignment
Partition - Odd Aligned
Disc
Max LBA
Starting LBA is Odd
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Large Sector Deployment Industry not Individual
Large Sector Deployment
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Response
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Standardization T13 Identify Device
Identify Device Data
Word 106
Physical Sector Size / Logical Sector Size
Word 117
Words Per Logical Sector
Word 118
Alignment of logical blocks within physical sector
Word 209
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Standardization T13 Identify Device
Identify Device Data
Physical Sector Size / Logical Sector Size
Word 117
Key 01 Word 209 is Valid Key ltgt 01 Word
209 Not Valid
Words Per Logical Sector
Word 118
Word 209
Alignment of logical blocks within physical sector
n
Key
15
14
13
0
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Microsoft Vista
Identify Device
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4K Alignment - Performance
Partition - Aligned
Disc
Starting LBA aligned
With a 1K Drive with 512 Byte Emulation on XP On
aligned partitions, most commands started on a
physical boundary Most commands ended on physical
boundary (most commands even length)
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Vista Observed Alignment
ID Word 209 Offset 0
Majority of runts appear to be eliminated with
proper alignment under Vista.
Some runts (requiring R-M-W under 512B emulation
mode) remain. These are understood to be File
System updates and not file access.
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Industry Timeline
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Journaling Concern
Journaling assumes 512 byte sectors. (Also
assumes sequential LBAs are physically
sequential.)
Disc
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Summary

• Large sectors are required to continue the
  Capacity, Reliability and Cost curves in disc
  drives
• 512 byte emulation is required for some period to
  enable backward compatibility
• The transition is an industry transition and not
  a single supplier transition
• Remaining Actions to Close
• Performance Mitigation/Acceptance due to
  remaining misalignment
• Closing Journaling Application Concerns
• Acceptance of Legacy Performance