Arla—a really likeable AFS-client Arla—a really likeable AFS-client
Johan Danielsson free Parallelldatorcentrum, KTH [email protected]
Assar Westerlund portable Swedish Institute of Computer Science [email protected] efficient
supports disconnected operation and encryption of the data stream
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What is AFS? AFS (cont.)
a world-wide distributed file system files are stored at dedicated file servers
also known as Andrew File System untrusted clients (cache managers) cache files on local disk
originally developed at CMU clients have to prove themselves to servers
later commercialised by Transarc
currently 150 public cells around the world
3 4 Consistency in AFS Implementation of Arla
when retrieving a file, the client gets a promise a kernel module (xfs) that the server will notify it before changing the
a user-level daemon (arlad) file
these communicate by sending messages over a the notification is called a callback character device
allows the client to read cached files without any network activity
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Advantages Kernel module (xfs)
easier development small, 5000 lines, 32 KB on i386
better portability implements
better development tools a system call
possible to use normal libraries a character device
a virtual file system Disadvantages performance?
7 8 Implementation (cont.) Performance
network UFS cold Arla cold Arla warm /bin/ls arlad (I) mkdir 22 3 (II) cp 61811 User-level (III) r.stat 22 3 (IV) r.grep 55 5 (V) compile 34 36 34
VFS XFS Kernel (elapsed time in seconds of Andrew Benchmark on a ThinkPad 560)
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Portability Portability (cont.)
Kernel modules for:
10% operating system dependent
SunOS lwp requires machine-specific context switch
code Solaris
NetBSD, FreeBSD, OpenBSD daemon runs on any Unix-like system
AIX worksonNTwithcygwin32
HP-UX
Digital Unix
11 12 Security and Encryption Disconnected operation
Kerberos 4-based (rxkad) allow file system operations without network connectivity
implementation written outside US read from already cached data
supports encryption of all data write operations to a log and replay later
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Disconnected operation (cont.) Future work
fetch on miss no fetch on miss consistent connected N/A more performance not consistent fetch-only disconnected
more platforms
more disconnected operations
file + database servers
15 16 Acknowledgments Availability
It’s all Bjorn¨ Gronvall’s¨ fault http://www.stacken.kth.se/projekt/arla/
Magnus Ahltorp Robert Burgess Artur Grabowski Love Hornquist-¨ Astrand˚ and lots of other people (see THANKS)
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