Transcript Slide 1

ATA Hybrid Disk drive
Nathan Obr, Jack Creasey
Microsoft Corporation
What is a Hybrid Disk Drive?
R/W
Spindle
drive
Add a non-volatile cache
Seek
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Dram
Cache
SOIC/
CPU
NV
Cache
Why Change the Disk Drive?
• Consumes up to 10% of the power budget for
mobile solutions
• Fragile, shock prone, low MTBF in mobile
systems
• Failure may result in user data loss (expense is
hard to quantify)
• Slow power up (takes a long time to come ready)
• Seek and rotational latency is a performance
bottleneck
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Why is a Hybrid Drive Better?
• Instant access to data in NV Cache
– Faster Boot and Resume
• Read and Write disk data while drive is in
a low power state
– Reduce power by turning components off
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Hybrid Disk Drive Benefits
Up to 90% Power Saving
when powered down
R/W
Spindle
drive
Read and Write instantly
while spindle stopped
Seek
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Dram
Cache
SOIC/
CPU
NV
Cache
Assumptions for Hybrid Disk
• The Operating System with its advanced
memory management is the best place to
cache read data (but not write data)
• The NV Cache is more appropriate for write
data
• NV Cache should be => 64MB
• The OS should be able to programmatically
define data (LBAs) to be Pinned in the NV
Cache
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Power Saving
• 87% reduction in power can be achieved (1.75W)
• Assumptions
– Pavg active = ~2W (measured)
– Pavg with Flash write buffer and Windows Longhorn kernel = 0.25W
(calculated)
• Toff = 600s @ .18W
• Ton = 18s @ 2.5W
– Ton = spin up time (5s) + Flash buffer flush time (13s)
» Flash buffer size = 128MB
» Transfer rate = 10MB/s
Power (W)
3
2
1
Toff > 600s
Ton 18s
Pavg with disk platter in use = 2.0W
Power reduced 1.75W
Pavg with flash write buffer = .25W
Time
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ATA Requirements
• We need to investigate both PATA and SATA
interfaces
• We need to plan commands for:
– Device identification – how big is the cache and
what power modes are supported?
– Set Features – enable or disable use of the NV
Cache
– Entering the NV Cache power mode
– Leaving the NV Cache power mode
– Spindle on timer
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ATA Requirements (cont’d)
• We need to plan commands for:
– Pinning (add and remove) LBAs in NV Cache
– Synchronizing the NV Cache with magnetic
media
– Query LBAs in NV Cache
– Query cache misses for access profiling
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Next Steps
• Development of a useable ATA command
set in process
• Disk drive manufacturers investigating
design options for Hybrid drives
• Microsoft analyzing benefits in future
versions of the Windows operating system
Copyright© Microsoft Corporation 2005