Parallax Dutch Meyer University of British Columbia - - PowerPoint PPT Presentation

Parallax

Dutch Meyer

University of British Columbia dmeyer@cs.ubc.ca

The Plan

 Virtual Machines and Storage  Parallax Feature Overview  Technical Design  System Evaluation  Conclusion

Parallax is a Storage Service

Observations on Naïve storage

 Virtual machines can be created and

destroyed easily - storage can’t

 VM encapsulation make capturing whole-

machine state attractive, but capturing a whole disk image is slow

 Giving similar VMs similar disk images

results in wasted space

Our Research Questions

 How do we make volume provisioning

agile enough to match VM creation?

 Can we capture whole-disk state at near-

continuous granularity?

 How much data redundancy can we

eliminate?

 How much overhead to do all of this well?

Parallax storage system

 Use snapshots as a unifying tool for

 Provisioning new volumes  Data sharing  Low overhead state capture and backup

 Allow block-level layout optimization  Allow disconnected/degraded operation  Compatibility due to VM based architecture

• perating at the block level

Snapshots

 Data Protection

 Low Granularity (eg days)

 “What if” configuration and testing  Backup

 High Granularity (eg ms)

 Legal compliance  Paranoia

 Time Travel – By capturing whole-machine state

at high frequency, we can revisit previous machine states

Provisioning via Gold Mastering

 Use snapshots to create a copy of some

reference volume, which can be further specialized

 Requirements include

Global availability Efficient operation No hard limits on the number of volumes

Data Sharing

 Commonly derived disks can share

common data

 Sharing is read-only, COW when data is

modified

 We can further eliminate redundancy by

detecting duplicate blocks and deduping them (current focus)

Parallax Implementation

 Building Virtual Disks  Locking and Synchronization  Storage Services

System Review

 Parallax engine is a user-mode tapdisk

driver for block management

 Provides services to any VM sharing the

same physical machine

 Federates across multiple physical

machines to share a single volume of storage

Building Virtual Disks

 Flexibility in block placement is essential

to providing disk isolation

 Parallax uses a radix tree to facilitate this

Fixed height Root is linked to a disk image Nodes are disk blocks, containing an array of

pointers

Radix Nodes and Trees

Taking A Snapshot

IO Batching

 Parallax follows the semantics of a physical disk

 Simultaneous requests may be completed in any order  Must retain “crash consistency”

 Updating radix trees can involve several IO operations

 Batching becomes essential to maintaining performance  Ordering constraints are imposed for crash consistency

 We use a dependency tracking system to issue writes in

the correct order

 Writes are aggressively pipelined – similar to instruction

scheduling

Parallax Implementation

 Building Virtual Disks  Locking and Synchronization  Storage Services

Federating Physical Machines

 All machines share a single disk  Some synchronization is required between

physical machines

 Data plane is protected through long lived

coarse grained allocation

 Control plane requires a lock manager

Lock Management

 Current System has 3 contentious locks

Creating a virtual disk Claiming a virtual disk Requesting a new extent

 In practice these locks are very infrequent  It is possible to further limit contention in

• ur design

Parallax Implementation

 Building Virtual Disks  Locking and Synchronization  Storage Service

Degraded Operation

Evaluation: Performance

Per Request Latency System Throughput

Evaluation: Snapshots

Storage Overheads Snapshot overhead

Conclusion

 We can use VM based encapsulation to

extend the services normally provided in a storage stack

 Despite using several potentially high-

• verhead techniques, parallax achieves

reasonable performance

Future Work

 Working on deduping, layout optimization  Expose features to aware file systems  More storage services for VMs: caching,

encryption, etc.

 General release

End of Presentation

 Thanks!  Questions?

Extents

 We wish to minimize contention for the

shared disk

 The simple approach is to partition the

disk into large extents which can be given exclusively to individuals

 We use a 2GB extent size currently

Translating: Virtual to Physical

01011100 0001 01011100 0001

Root

0101

A

1 1

B

0001

C