Petal and Frangipani

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Petal and Frangipani
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Petal/Frangipani
NFS
NAS
Frangipani
SAN
Petal
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Petal/Frangipani
Untrusted OS-agnostic
FS semantics Sharing/coordination
Disk aggregation (bricks) Filesystem-agnostic Re
covery and reconfiguration Load balancing Chained
declustering Snapshots Does not control sharing
Each cloud may resize or reconfigure
independently. What indirection is required to
make this happen, and where is it?
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Remaining Slides

• The following slides have been borrowed from the
  Petal and Frangipani presentations, which were
  available on the Web until Compaq SRC dissolved.
  This material is owned by Ed Lee, Chandu
  Thekkath, and the other authors of the work. The
  Frangipani material is still available through
  Chandu Thekkaths site at www.thekkath.org.
• For CPS 212, several issues are important
• Understand the role of each layer in the
  previous slides, and the strengths and
  limitations of each layer as a basis for
  innovating behind its interface (NAS/SAN).
• Understand the concepts of virtual disks and a
  cluster file system embodied in Petal and
  Frangipani.
• Understand the similarities/differences between
  Petal and the other reconfigurable cluster
  service work we have studied DDS and Porcupine.
• Understand how the features of Petal simplify
  the design of a scalable cluster file system
  (Frangipani) above it.
• Understand the nature, purpose, and role of the
  three key design elements added for Frangipani
  leased locks, a write-ownership consistent
  caching protocol, and server logging for recovery.

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Petal Distributed Virtual Disks

• Systems Research Center
• Digital Equipment Corporation
• Edward K. Lee
• Chandramohan A. Thekkath

12/21/2020
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Logical System View
AdvFS
NT FS
PC FS
UFS
Scalable Network
Petal
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Physical System View
Parallel Database or Cluster File System
Scalable Network
/dev/shared1
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Virtual Disks

• Each disk provides 264 byte address space.
• Created and destroyed on demand.
• Allocates disk storage on demand.
• Snapshots via copy-on-write.
• Online incremental reconfiguration.

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Virtual to Physical Translation
Server 0
Server 1
Server 2
Server 3
Virtual Disk Directory
vdiskID
offset
GMap
PMap0
PMap1
PMap2
PMap3
(disk, diskOffset)
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Global State Management

• Based on Leslie Lamports Paxos algorithm.
• Global state is replicated across all servers.
• Consistent in the face of server network
  failures.
• A majority is needed to update global state.
• Any server can be added/removed in the presence
  of failed servers.

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Fault-Tolerant Global Operations

• Create/Delete virtual disks.
• Snapshot virtual disks.
• Add/Remove servers.
• Reconfigure virtual disks.

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Data Placement Redundancy

• Supports non-redundant and chained-declustered
  virtual disks.
• Parity can be supported if desired.
• Chained-declustering tolerates any single
  component failure.
• Tolerates many common multiple failures.
• Throughput scales linearly with additional
  servers.
• Throughput degrades gracefully with failures.

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Chained Declustering
Server0
Server1
Server2
Server3
D0
D1
D2
D3
D3
D0
D1
D2
D4
D5
D6
D7
D7
D4
D5
D6
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Chained Declustering
Server0
Server1
Server2
Server3
D0
D2
D3
D1
D3
D1
D2
D0
D4
D6
D7
D5
D7
D5
D6
D4
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The Prototype

• Digital ATM network.
• 155 Mbit/s per link.
• 8 AlphaStation Model 600.
• 333 MHz Alpha running Digital Unix.
• 72 RZ29 disks.
• 4.3 GB, 3.5 inch, fast SCSI (10MB/s).
• 9 ms avg. seek, 6 MB/s sustained transfer rate.
• Unix kernel device driver.
• User-level Petal servers.

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The Prototype

src-ss1
src-ss2
src-ss8
/dev/vdisk1
/dev/vdisk1
/dev/vdisk1
/dev/vdisk1

petal1
petal2
petal8
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Throughput Scaling
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Virtual Disk Reconfiguration
8 servers
6 servers
virtual disk w/ 1GB of allocated storage 8KB
reads writes
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Frangipani A Scalable Distributed File System

• C. A. Thekkath, T. Mann, and E. K. Lee
• Systems Research Center
• Digital Equipment Corporation

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Why Not An Old File System on Petal?

• Traditional file systems (e.g., UFS, AdvFS)
  cannot share a block device
• The machine that runs the file system can become
  a bottleneck

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Frangipani

• Behaves like a local file system
• multiple machines cooperatively managea Petal
  disk
• users on any machine see a consistentview of
  data
• Exhibits good performance, scaling, and load
  balancing
• Easy to administer

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Ease of Administration

• Frangipani machines are modular
• can be added and deleted transparently
• Common free space pool
• users dont have to be moved
• Automatically recovers from crashes
• Consistent backup without halting the system

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Components of Frangipani

• File system core
• implements the Digital Unix vnode interface
• uses the Digital Unix Unified Buffer Cache
• exploits Petals large virtual space
• Locks with leases
• Write-ahead redo log

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Locks

• Multiple reader/single writer
• Locks are moderately coarse-grained
• protects entire file or directory
• Dirty data is written to disk before lock is
  given to another machine
• Each machine aggressively caches locks
• uses lease timeouts for lock recovery

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Logging

• Frangipani uses a write ahead redo log for
  metadata
• log records are kept on Petal
• Data is written to Petal
• on sync, fsync, or every 30 seconds
• on lock revocation or when the log wraps
• Each machine has a separate log
• reduces contention
• independent recovery

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Recovery

• Recovery is initiated by the lock service
• Recovery can be carried out on any machine
• log is distributed and available via Petal