Transcript Your Desktop on Your Keychain Ted Wobber MSR Silicon Valley with Muthukarrupan Annamalai, Andrew Birrell, and Dennis Fetterly.

Your Desktop on Your Keychain
Ted Wobber
MSR Silicon Valley
with Muthukarrupan Annamalai,
Andrew Birrell, and Dennis Fetterly
Hardware vs. Desktop State
• Computers are (increasingly) everywhere
– In furniture/kiosks/environment?
• New form factors for carrying state:
– Keychains, cellphones, watches
• Can we make desktop state portable without
also carrying the computer hardware?
• Desktop state = user preferences +
user data + applications
Who cares??
• Corporations and other large organizations
– Moving between offices, sites
– Office-sharing
– Work-at-home scenarios
• Consumers in general
– But kiosk infrastructure and security is a barrier
• Emerging markets
– Desktop hardware is scarce
– Benefit may outweigh security risk
Models of Desktop Portability
• Laptops
• Roaming profiles
• Remote desktop
Laptops
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Laptops are (usually) bulky and fragile
Expensive to purchase and to manage
Prone to theft
Once stolen, data is (often) vulnerable
Backup can be haphazard
• But, laptops are self contained and offer a
valuable platform for disconnected environments
Roaming Profiles
• Applications don’t roam
• In Windows, difficult to separate user,
application, and machine-specific state
• Slow, bandwidth intensive
• Difficult outside single admin domain
• Security of host machine?
Remote Desktops
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Needs strong connectivity
Latency-sensitive
Difficult outside single admin domain
Needs managed server to provide RDP service
– Most desktop PCs aren’t “professionally managed”
• Local devices?
Flash Changes the Equation
• Current cost: 1GB = ~$80
• Still following Moore’s Law
• Read/Write performance approaching disk
• Modern flash has built-in wear-leveling
– Max write limitations are rarely a problem
• For this talk: Flash == USB Flash Device
Flash Statistics (estimate)
• Projected shipments 60-120 million units in 2005
• 2 GB in ’04; 4GB+ in ’05.
• Estimated revenue on NAND-based Flash at $9.2 billion
in ‘06 timeframe
• NAND Read/Write speeds are slated to increase as
follows:
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‘04 read 8 MB/s; write 6.5MB/s.
’05 read. 23 MB/s; write 16MB/s.
‘06 read 40 MB/s; write 28 MB/s.
‘07 guesstimates are 100MB/s using multiple NAND chips and cache.
• Already being extended with onboard CPU, memory,
wireless, etc.
Carry user state cache on flash
• Similar problems to roaming profiles:
– Applications don’t roam
– In Windows, difficult to separate user, application, and
machine-specific state
– Slow, bandwidth intensive
– Difficult outside single admin domain
– Security of host machine?
Boot from Flash
• Drivers
– Problem gets worse with age of installation
• Flash capacity (in short term)
– Size of OS + apps a problem
– What happens when disk is full?
• Machine state (e.g. hibernation) is non portable
• Backup?
Our Solution
• Host machine runs virtual machine monitor
• User runs in a virtual machine (VirtualPC)
• Virtual disk is a “server in the sky”
– Remote disk handles overflow and backup
• The flash acts as:
– A persistent cache/log of virtual disk
– Storage for virtual machine state
• Local disk as “lookaside” for virtual disk content
Why Virtualization?
• Eliminates host-specific customization
– (e.g. drivers, etc)
• Easy to encapsulate and move VM state
• Fewer “moving parts” on host
– Easier to manage/secure: VMM is only requirement
• Development cost (our prototype < 1 kloc)
– Simple to customize basic abstractions
• Good performance and getting better
– Hardware support of virtualization
• Other platforms? XBox2?
• Virtual disks make provisioning new users easy
Differencing Disks
• Compact representation of overlaid content
• Standard feature of virtual machines
• Convenient for shared disk provisioning
– E.g. multiple users share same base disk
VMM sees:
Differencing Disk(s):
Base Disk:
Why a network connection?
• At least for now, flash drives are too small
– With Windows+Office it’s easy to overflow a 1GB disk
• Backup is automatic
– Server can keep multiple restore points
• Perhaps this requirement can be eliminated in
the future
Kiosk Architecture
VMM Host
Your Computing
Environment
Flash Disk
Write Log
VirtualPC
Disk as seen by
your programs
Read Cache
File Server
Composed of ...
User-Specific
Differencing Disk
Lookaside Images (~Base Disk)
Base Disk Image
Disk Writes
VMM Host
Your Computing
Environment
Flash Disk
Write Log
VirtualPC
Read Cache
Disk as seen by
your programs
File Server
Composed of ...
User-Specific
Differencing Disk
Lookaside Images (~Base Disk)
Base Disk Image
Disk Reads
VMM Host
Flash Disk
Your Computing
Environment
1
Write Log
VirtualPC
3 Read Cache
Disk as seen by
your programs
Composed of ...
2
File Server
4
User-Specific
Differencing Disk
5
Lookaside Images (~Base Disk)
Base Disk Image
Demo
A bit more detail
• Persistent state on flash
– Virtual machine state (optional)
– Writes logged since last merge
– Fingerprint for every 16K chunk in remote virtual disk
• MD5 as a fingerprinting algorithm (128 bits)
– Set of cached 16K chunks
Persistent, in flash
A: Chunk number to Fingerprint map (for entire disk)
FP0
FP1
…
FPN
B: Write Log (sectors)
C: Read Cache (chunks)
7
Data for chunk 7
114 Data for chunk 114
35
Data for chunk 35
…
…..
27
Data for sector 27
3
Data for sector 3
17
Data for sector 17
…
…..
Volatile, in memory
A: Chunk number to Fingerprint map (for entire disk)
FP0
B: FP to Read Cache
hash table (chunks)
FP0
FP1
FP7
7
Chunk 7
FP114
114
Chunk 114
FP35
35
Chunk 35
…
…
…..
…..
D: FP to Static Disk
hash table (chunks)
…
FP1
…
FPN
C: Write log
hash table (sectors)
FPN
27 Sector 27
27
3 Sector 3
3
17 Sector 17
17
…
…..
…..
…
FP
FP
FP
…
…..
Lookaside Image
Updating the Fingerprint Map
• Must compute new chunk fingerprints
• Partial chunks requires unwritten sectors
Read old chunk
New FP
Add new sectors
What’s actually implemented
• Write “log” is a differencing disk on flash
– Differencing drive chain:
• Flash differencing disk →
Home differencing disk → Home base disk
• Manual merging only
– No automatic updates in background
– Standard VirtualPC “merge to parent”
– Merge updates read cache
• Read cache is untuned
Potential Drawbacks
• Security of kiosk machine
• Infrastructure rollout
• Connectivity requirement
– As flash sizes grow, need for online server decreases
– Range of solutions possible depending on size
• Artifacts of virtualization
– Availability of pass-through devices
– Fancy graphics devices unavailable
• Ensuring that working set fits within the cache
Performance Bottlenecks
• Windows likes to write to disk
– Flash fills up quickly
– Differencing disk overlays >10% of base image
• Read/write performance:
– 4K Reads (sequential or random) ~.8 ms
– 4K Writes (sequential) ~ 1.0 ms
– 4K Writes (random) > 20ms !!!!
We have confirmed this by analyzing traffic at the USB driver
level. The root cause of the 20 ms latency is a mystery. Our
observations are inconsistent with NAND-memory specs.
Optimizations (current)
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Fast-launch defragmentation turned off
Paging disabled
Last-access date on files disabled
Various services turned off
No anti-virus / indexing
Optimizations (possible)
• Implement real log (for sequentiality)
– With redundant write elimination
• RAM disk for temporary files (e.g. IE)
• Keep guest-OS NTFS log on local disk
• Log writes to on-kiosk differencing disk …
periodic sync to flash
• Network read/write compression
• Virtual disk snapshots
Security
• Primary threats:
– Bogus, tapped, or otherwise compromised kiosk
– Theft of device
• But, this is a computer:
ASIC or processor
NAND Memory
Trusting the Kiosk
• Non-technical considerations
– Physical security
• Site security (e.g. within a corporation)
• Physical packaging and locks (like an ATM)
• Kiosk owner must be accountable
• Technical solutions
– NGSCB / Trusted Boot / Attestation
• Small footprint (e.g. just OS+VMM) helps here
– User-specific, unforgeable visual feedback
– External helper device with UI (e.g. cellphone)
Protecting Against Theft
• On-flash encryption, “unlocks” data only after:
– Flash authenticates kiosk
– Flash informs user that kiosk is OK
– User gives credentials (e.g. password or biometric)
• Lock-out on repetitive failure
• Host-based encryption is also possible
– But gives weaker guarantees
• User can roll back to disk state on server
Related Projects
• Internet suspend/resume
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CMU / Intel Labs
Virtual machine serial portability
Supported by Coda-like distributed FS
Flash for read optimization
• Stanford “Collective” project
– Portable virtual machine
– Virtual state/disk “capsule” hierarchy
Conclusions
• New model for desktop portability
• Augments range of existing techniques
• Spectrum of flash-based solutions
• Looking for ways we can help product efforts
• Haven’t explored business/market ramifications
• Highlights two growing market forces:
Flash and Virtualization