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YFS: An Introduction to the next / afs ®. Jeffrey Altman, Daria Brashear, Marc Dionne , & Simon Wilkinson Your File System Inc . and Your File System Ltd. 2014 European AFS and Kerberos Conference. Your File System.

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YFS: An Introduction to the next /afs®

Jeffrey Altman, Daria Brashear, Marc Dionne, & Simon Wilkinson

Your File System Inc. and Your File System Ltd.

2014 European AFS and Kerberos Conference


Your File System

  • Your File System Inc. (YFSI) is a New York State Corporation with HQ in Manhattan and registered as a business entity in Canada
  • Your File System Ltd is a wholly owned subsidiary of YFSI with HQ in London
  • YFSI is privately owned and operated
  • YFSI is a Red Hat Partner ISV

The /afs® Vision

  • Location Transparency: one name space
  • User Mobility: access from any device
  • Security: Flexible model for authentication, privacy, data protection and access control
  • Availability: Temporary loss to small groups for short time periods
  • Integrity: No user initiated backups
  • Heterogeneity: Multiplatform
  • Self service: Low Help Desk costs
  • Atomic Publishing: Software, documentation, web sites, ..
  • Real time collaboration: Distributed File Locking
  • Distributed Administration

AFS® is 30 years old

The vision was decades ahead of its time in 1983

The implementation is decades behind in 2014


The Price of Inaction

  • Limited network throughput
  • Increased call processing latency
  • Decreased service reliability and availability
  • Elevated risk of distributed deadlocks
  • Inability to use full capability of available hardware
  • Failure to keep up with competing technologies

That /afs is still in use today is a credit to its vision and the strength of its architecture.


13 Years of Open Source

Major system rewrites are few and far between

“Contractor Model of Support” leads to many small and localized changes

A lack of consistent vision and quality control

Few incentives to invest in the next 30 years


The YFS Vision for /afs

  • Application Transparency
    • Be a Tier One file system on all major OSes
  • Embrace multi-producer, multi-consumer work flows
  • Extended Integrity: Disaster Recovery

The YFS Vision for /afs

  • Be performance competitive
    • Lustre, GPFS, Panasas, …
  • Best of breed data security
  • Improved Ease of Use
  • Designed for the long term

Preserving the old while providing the new

  • Improved performance with existing hardware
  • Cost reductions due to hardware consolidation
  • Zero data loss as part of a transition
  • No flag day required
    • Mixed deployments are encouraged

Performance: Why Does it Matter?

Performance issues restrict the jobs that sites are willing to run in /afs

Deploying excessive hardware to solve load distribution and fairness problems is expensive

Support for multiple file systems costs money, requires additional staff, can result in data duplication and out of sync issues


RX Performance

  • Reduced contention in the listener thread
    • 10 gbit network interface saturation
  • 255 packet window size (per call) without degradation
    • Order of magnitude faster on high latency links
  • Dynamic Thread Pools
    • Thread Count limited by OS resources

Scalability: Name Space Growth

  • 64-bit volume IDs
  • 96-bit (79 octillion) vnode IDs
  • 64-bit,100ns granular timestamps
    • 2038 ready
  • Ubik databases extensible up to 16 exabytes
  • Partitions, volumes and quotas tracked up to 16 zettabytes

Performance: Message Flow Optimizations

  • Optimized Cache Manager handshakes
  • Volume Status Information
    • Reduces number of GetVolumeStatus RPCs
    • Permits RW / RO data cache sharing
    • Improved caching of RO volume per user permissions
      • Fewer FetchStatus RPCs for RO volumes

Performance: Fileserver

  • Host and callback package rewritten
    • Significantly faster callback breaks
  • Vnode lock contention dramatically reduced
  • Distributed writing to shared data sets now possible

Performance: POSIX O_DIRECT

Open mode supported on some OSes

Bypasses VFS cache and AFS cache for both read and write

No file threshold to tune

Data is copied directly to the caller, or directly from the caller to the file server


Security: Why Does it Matter?

  • Data breaches and exposures are followed by a high cost
    • Public Relations Nightmare
    • Costs of Identity Theft Detection Services (in U.S.)
    • Loss of employment for key staff members
    • Organizational reorganization
    • Disruption of core mission when forced to address security concerns in crisis mode

What is YFS Security?

  • Multi-layered policies
    • Flexibility for self service end users
    • System administrator controls
  • Network Security
  • Reduced Information Exposure
  • Minimal Privilege Services

Security: End Users

  • Self Service Group Management
  • Per-Object ACLs
    • Cross directory hard links now permitted

Security: System Administrators

  • Volume ACLs
    • Limits the permissions that end users can grant

Security: System Administrators

  • Volume Security Policy
    • Per-Volume minimum acceptable rx connection security properties
  • File Server Security Policy
    • Per-server minimum acceptable rx connection security properties
    • Only volumes with weaker or equivalent security policy can be attached, moved to, or restored to.

Security: Network

  • YFS RXGK Security Class
    • GSS Kerberos 5 authentication
    • AES-256 wire privacy and integrity protection
  • Cell wide key for DB servers
  • Individual keys for file servers
  • Per-host keys for BOS Overseer Service

Security: Callbacks

  • YFS protects the callback channel with AES-256 privacy and integrity protection
    • when rxgk is used for the incoming connection
    • Avoids leaking information about volume and file ids accessed by a client
    • Prevents forged messages from invalidate callback state

Security: Minimal Privileges

  • Server Processes execute under a daemon account
    • Not Root

Security: Keyed CMs & Machine IDs

  • Cache Managers can be issued
    • a Kerberos keytab
    • a Protection DB Machine ID
  • Keyed Cache Managers can use privacy for all connections
  • Machines IDs are similar to User IDs
    • Can be placed on ACLs and added to Groups
    • But are not included in system:authuser

File System Extensions

  • Per File ACLs
  • Cross directory hard links

Extensions for Microsoft Windows

  • Mandatory Locks
    • Advisory locks are not enforced by the file server
  • Symlink Updates
    • Reparse Points can be updated without FileID change
  • CreateFile with Lock
    • Avoids races when simulating OpLock semantics

Command Output Clarity

  • Modifications to human readable and machine readable output
  • vos examine, listvol, rxdebug, xstat_fs, …
    • Consolidate output
    • Introduce consistency across command options
  • Machine readable output –format is not human formatted
    • All fields are now separated by single tabs
    • Easy to import into spreadsheets and databases

Library Cleanup

  • All libraries are thread safe
  • Built using libtool
  • Intended for use implementing language bindings


  • A library to obtain tokens
    • rxkad
    • yfs-rxgk
  • aklog is a wrapper
  • Can be linked to pam modules

Automated Windows Domain Token Acquisition

  • Triggered by access denied errors
  • Automatic Token acquisition using Logon Session Kerberos Credentials
  • Works with all applications that use
    • WNet API: Network Providers
    • Shell API: Explorer, Office, anything with an Open dialog

Why are Deployment and Configuration Important?

Simplify Server Configuration

Provide Extensibility for New Features

BOS command lines are limited in length

Permit the construction of flexible test suites


Flexible Configuration

  • Greatly improved configuration flexibility and convenience
    • Custom file layouts are possible
    • All settings centralized in a single configuration area, single file or directory
    • A configuration directory can ease distribution of custom options
    • All command line options can be set in configuration

Test Suites

  • Goal
    • Provide a test for every new feature, library function, RPC
    • Provide a test with every bug fix, if possible
  • Requirements
    • Ability to spin up the various servers and provide a test configuration
    • All tests must be able to run as a regular user
    • Must be able to serve test data not necessarily under /vicep*

Extensive test suite coverage

A complete test cell can spin up in a few seconds

Many tests spin up a cell and destroy it when done, maintaining test independence

Client testing through libafscp and fuse client

All new features require tests before merging


Sample systemdyfs-server.service


Description=YFS Server Service



ExecStart=/usr/local/sbin/bosserver -config /s/yfs/server/yfs-server.conf -nofork

ExecStop=/usr/local/bin/bos -config /s/yfs/server/yfs-server.conf shutdown -wait -localauth





Sample file layout

[marco@hurricane /s/yfs/server ]$ ls -l

total 60

drwxr-xr-x. 2 yfsyfs 4096 Mar 23 04:00 bos

-rw-r--r--. 1 yfsyfs 526 Jul 15 2013 bos.keytab

-rwxr-xr-x. 1 yfsyfs 26 Jul 15 2013 cacheinfo

drwxrwxr-x. 6 yfsyfs 4096 Jan 11 15:36 data

drwxrwx---. 2 yfsyfs 4096 Oct 25 10:47 db

-rw-r--r--. 1 yfsyfs 4 Jan 6 09:52 KeyFile

-rw-r--r--. 1 yfsyfs 144 Jan 6 09:52 KeyFileExt

drwxrwx---. 2 yfsyfs 4096 Mar 25 10:28 local

drwxrwxrwx. 2 yfsyfs 12288 Mar 25 10:29 logs

-rw-r--r--. 1 yfsyfs 15 Sep 12 2013 ThisCell

-rw-r--r--. 1 yfsyfs 114 Dec 19 16:56 UserList

-rw-r-----. 1 yfsyfs 2000 Aug 5 2013 vl.keytab

drwxrwxr-x. 2 yfsyfs 4096 Mar 26 18:25 yfs-server.conf

[marco@hurricane /s/yfs/server ]$ ls -l yfs-server.conf/

total 8

-rw-r--r--. 1 yfsyfs 645 Mar 26 18:25 cellservdb.conf

-rw-rw-r--. 1 yfsyfs 792 Mar 4 15:48 yfs-server.conf


Sample cellservdb.conf = {

description = "GCO Public CellServDB 23 Apr 2008"

servers = { = {

addr =

} = {

addr =

} = {

addr =




[cells] = {

description = "Test cell"

servers = { = {

addr =



} = {

description = "Marc's cell"

servers = { = {

addr =





Sample server configuration


keytab = /s/yfs/server/vl.keytab

auditlog = /s/yfs/server/logs/audVl


d = 125

auditlog = /s/yfs/server/logs/audVol


auditlog = /s/yfs/server/logs/audBos


auditlog = /s/yfs/server/logs/audPt


auditlog = /s/yfs/server/logs/audSalv


auditlog = /s/yfs/server/logs/audSalvserv


SERVER_ETC_DIR = /s/yfs/server

SERVER_DB_DIR = /s/yfs/server/db

SERVER_LOGS_DIR = /s/yfs/server/logs

SERVER_BOSCONFIG_DIR = /s/yfs/server/bos

SERVER_LOCAL_DIR = /s/yfs/server/local

SERVER_PART_PREFIX_DIR = /s/yfs/server/data


d = 125

p = 200

nojumbo =

auditlog = /s/yfs/server/logs/audFile

security = yfs-rxgk:cryptrxkad:clearrxnullrxkad:crypt


Why Packaging Changes are Important?

Installation is the initial experience an end user has with the product

If the installation process is frustrating, the end user is likely to be unhappy with the product

Lack of digital signatures can block the installation of a package or trigger a frightening dialog


Installation Packages

  • New installation packages
    • Windows
    • OSX
    • Linux
      • Debian
      • Fedora
      • RHEL6 and RHEL7

Microsoft Windows®

  • Single installer
    • 64-bit and 32-bit components
    • Heimdal Side by Side Assembly
    • Heimdal Command Line tools
    • Automatic Cache Sizing
  • All components digitally signed
    • Microsoft Cross Signing of Drivers


  • Flat package
  • Integral packages for client, server and development
  • Digital signatures on the package, the kext and the binaries using Apple-issued certificate


New packaging for Debian, Fedora and RHEL

Integral packages for client, db services, and file service

Digital signatures on installation packages


Dual Protocol Stacks

  • Allows advanced features while maintaining backwards compatibility with AFS®
  • AFS protocol suite has all of the capabilities and limitations of OpenAFS
  • YFS features only available on YFS protocol suite
    • rxgk, file server, vol server, vl server, pt server enhancements
  • Transparent negotiation of protocol suite

Mixed Mode Cells

  • Two cell types are defined:
    • AFS cell deploys OpenAFS or IBM AFS vlservers
    • YFS cell deploys the YFS location server
  • OpenAFS and YFS File Servers can be joined to either cell

YFS Client in AFS Cell

No support for RXGK, AES-256

No support for file server security policies


YFS Server in AFS Cell

Improved RX Performance for writes

No Rxgk

Volume IDs restricted to AFS limits

Security Policies cannot be enforced

Only AFS compatible capabilities can be registered

IPv6 addresses cannot be registered


YFS File Server in AFS cell




AFS volume







YFS Server in AFS Cell

Improved RX Performance for writes

No Rxgk

Volume IDs restricted to AFS limits

Security Policies cannot be enforced

Only AFS compatible capabilities can be registered

IPv6 addresses cannot be registered


AFS Client in YFS Cell

No support for RXGK, AES-256

No support for file server security policies

Volumes with ID above 232-1 inaccessible

Mandatory locks cannot be requested but will be enforced

Volume sizes and quotas >231KB will be faked

Other restrictions as required to enforce security policies


AFS File Server in YFS cell





AFS volume






YFS volume




AFS and YFS Volserver Compatibility

  • RW volumes on YFS server cannot be replicated to AFS server
  • Volumes containing YFS tags cannot be moved to an AFS server
    • ACL Data
    • Volume Attributes (ACL or Security Policy)
  • Data transfers protected with Rxkad and Fcrypt
  • RX performance improved in YFS to AFS direction
yfs file server
YFS File Server

YFS POSIX attribute backend store

YFS protocol suite

AFS protocol suite


yfs protection server
YFS Protection Server

64 bit Ubik database

YFS protocol suite

AFS protocol suite


yfs location server
YFS Location Server

64 bit Ubik database



YFS protocol suite

AFS protocol suite




Updated man pages

New Quick Start Guides

Updated Administrator’s Guide


Export Licenses

The U.S. Government has classified YFS 1.x as a mass market product

Worldwide Export permitted with a few exceptions

No export restrictions on distribution by customers


YFS 1.0 Binary License

  • A full suite of clients and servers
    • Windows
    • OSX
    • iOS
    • RHEL5, RHEL6, RHEL7
    • Fedora
    • Debian
    • Solaris
    • AIX


  • Free updates to new releases (one year)
    • Every four month release cadence
  • Free security updates (two years)
  • Unlimited e-mail / web support (one year)
  • Cell performance evaluation (once per year)
  • Remote monitoring service (one year)


Cell (no replication)

1 Server (DB and File)

Base cell (replication)

4 DB Servers

4 File Servers

1000 User or Machine IDs

Unlimited Client devices

Additional Servers

Additional IDs

Annual purchases continuesupport

Non-redistribution Source code license available

Training (on-site or web)



General Availability End of May 2014

First update, September 2014


2014 Road Map

  • Feature Priorities
    • IPv6 enhancements
    • Rapid Partition Relocation
    • Extended Volume Names
    • New Directory Format
      • Unlimited Directory Sizes
      • Extended Attributes
      • Alternate Data Streams
    • Read/write Replication
    • Extended Callbacks

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