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OneFS distributed file system
The OneFS file system is a parallel distributed networked file system designed by Isilon Systems for use in its Isilon IQ storage appliances. OneFS is a FreeBSD variant and utilizes zsh as its shell. OneFS has its own specialized command set,〔("OneFS Command Line Reference" )〕 all of which (with the exceptions of the Isilon extensions to the Unix "ls" and "chmod" commands)〔("EMC Isilon Multiprotocol Data Access with a Unified Security Model" )〕 start with "isi", which is used to administer the system.
== On-disk Structure ==
All data structures in the OneFS file system maintain their own protection information. This means in the same filesystem, one file may be protected at +1 (basic parity protection) while another may be protected at +4 (resilient to four failures) while yet another file may be protected at 2x (mirroring); this feature is referred to as FlexProtect.〔("Data Protection and Backup" )〕 FlexProtect is also responsible for automatically rebuilding the data in the event of a failure. The protection levels available are based on the number of nodes in the cluster and follow the Reed Solomon Algorithm. Blocks for an individual file are spread across the nodes; for example, block 0 may be on Node 3, block 1 on Node 1, and the related parity block on Node 5. This allows entire nodes to fail without losing access to any data. File metadata, directories, snapshot structures, quotas structures, and a logical inode mapping structure are all based on mirrored B+ trees. Block addresses are generalized 64-bit pointers that reference (node, drive, blknum) tuples. The native block size is 8192 bytes; inodes are 512 bytes on disk.
One distinctive characteristic of OneFS is that metadata is spread throughout the nodes in a homogeneous fashion. There are no dedicated metadata servers. The only piece of metadata that is replicated on every node is the address list of root btree blocks of the inode mapping structure. Everything else can be found from that starting point, following the generalized 64-bit pointers.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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