ATOL: Global File System
Marek Grác
xgrac@f i.muni.cz
Red Hat Czech s.r.o. / Faculty of Informatics, Masaryk University
Advanced Topics of Linux Administration
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What is GFS?
►  Symmetric, shared-disk filesystem for cluster
►   Relies on cluster infrastructure
►•   Inter-machine locking (DLM) - cman, ccs, openAIS ►•   I/O fencing and recovery coordination
►   CLVMD to distribute LVM medata updates to cluster nodes
►   Metadata journaling, data journaling on per-file or per-directory basis
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What is GFS?
►  Shared file system
►  64-bit clean', POSIX compliant, ACL
►  Direct I/O capable, Online filesystem management
►  SELinux policy
►  Avoids central data structures
Run on mixed environment x86, ia64, amd64
►  Limits:
►•   100+ GFS client nodes
►   16TB on 32bit, 8EB on 64bit (support on multiple 8TB)
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Shared (GFS) vs Distributed Filesystem (AFS)
►  Whole file locking
►  One common journal
►  Save-on-close - writeQ only update the local cache copy on client
►  UNIX mode bits are ignored for group and other (provided by ACL)
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Create a GFS File system
►   Lock manager (lock_nolock, lock_dlm)
►   Lock file name (cluster_name:fs_name)
►   Number of journals (one per cluster node is needed)
►  gfs-tool, gfs.mount
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Context Dependent Path Names
►  Use of special directory link names (©hostname, Omach, Oos, Quid)
►  Symlink dependent on caller's context
►  Example: In -s /nfs/@hostname/sysinfo /nfs/sysinfo
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►  Create a GFS filesystem
►  Extend it and add one more journal
►  Use a CDPN
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► Themes:
►  GFS vs OCF Format:
►•  Short presentation (15-20 minutes; 5-7 slides) ►•   Paper containing comparision (1.000 words)
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