Developer(s)Isilon Systems
Full nameOneFS
Introduced2003; 21 years ago (2003) with OneFS 1.0 -- based on FreeBSD
Directory contentsB+ trees
File allocationB+ trees
Max volume size66PB+ (144+ nodes at 470TB+ each);[1] 65535 nodes theoretical limit
Max file size16TB
Max no. of filesCluster size dependent
Max filename length255 bytes
Max directory depth509 (suggested, to fit within PATH_MAX of 1023)[1]
Allowed filename
Many (UTF-8, EUC-JP, CP932, CP1252, ISO-8859-*, EUC-KR, CP949). Encoding is per-directory entry, not per-filesystem. So multiple encodings may be used in a single volume. UTF-8 is encouraged as normative. NUL and / are not allowed in individual directory entries in any encoding.
Dates recordedCreate time, rename time, mtime, ctime, atime
Date range1970 to 2038
Date resolutionNanosecond
ForksYes (extended attributes and Alternate Data Streams)
File system
Yes (POSIX permissions and NTFS ACLs)
Integrated with Self-encrypting Drives for encryption of "data at rest"[3]
Data deduplicationOffline only
Copy-on-writeYes (for snapshots)
operating systems

The OneFS File System is a parallel distributed networked file system designed by Isilon Systems and is the basis for the Isilon Scale-out Storage Platform.[3] The OneFS file system is controlled and managed by the OneFS Operating System, a FreeBSD variant.[3]

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.[4] 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. 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 (for disks with 512 byte sectors) or 8KB (for disks with 4KB sectors).

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.


The collection of computer hosts that comprise a OneFS System is referred to as a "cluster". A computer host that is a member of a OneFS cluster is referred to as a "node" (plural "nodes").

The nodes that comprise a OneFS System must be connected by a high performance, low-latency back-end network for optimal performance. OneFS 1.0-3.0 used Gigabit Ethernet as that back-end network. Starting with OneFS 3.5, Isilon offered InfiniBand models. From about 2007 until mid-2018, all nodes sold utilized an InfiniBand back-end. Starting with OneFS 8.1.0 and Gen6 models, Isilon again offers Ethernet back-end network (10, 25, 40, or 100 Gigabit).[5]

Data, metadata, locking, transaction, group management, allocation, and event traffic are communicated using an RPC mechanism traveling over the back-end network of the OneFS cluster. All data and metadata transfers are zero-copy. All modification operations to on-disk structures are transactional and journaled.


OneFS supports accessing stored files using common computer network protocols including NFS, CIFS/SMB, FTP, HTTP, and HDFS.[3] It can utilize non-local authentication such as Active Directory, LDAP, and NIS. It is capable of interfacing with external backup devices and applications that use NDMP protocol.[3]

OneFS Operating System

The OneFS File System is a proprietary file system that can only be managed and controlled by the FreeBSD-derived OneFS Operating System.[3]

zsh is the default login shell of the OneFS Operating System. OneFS presents a specialized command set to administer the OneFS File System.[6] Most specialized shell programs start with letters isi. Notable exceptions are the Isilon extensions to the FreeBSD ls and chmod programs.[7]


See also


  1. ^ a b "Isilon OneFS and IsilonSD Edge: Technical Specifications Guide" (PDF). Dell Inc. June 2018.
  2. ^ Adam Armstrong (12 February 2019). "Dell EMC Launches All-Flash Isilon F810". Flying Pig Ventures.
  3. ^ a b c d e f "Dell EMC Isilon OneFS Operating System - Powering the Isilon Scale-out Storage Platform" (PDF). 9.0. Dell Inc. February 2019.
  4. ^ "Data Protection and Backup"[dead link]
  5. ^ "Isilon Gen6 Performance" (PDF). Dell Inc.
  6. ^ "OneFS Command Line Reference"".[dead link]
  7. ^ Aqib Kazi (November 2018). "Isilon OneFS Authentication, Identity Management, & Authorization - Multiprotocol Data Access with a Unified Security Model" (PDF). Dell EMC.
  8. ^ a b c Determined by the __FreeBSD_version definition in /usr/include/sys/param.h. See FreeBSD Porter's Handbook for more information.
  9. ^ The FreeBSD Documentation Project. "18". FreeBSD Porter's Handbook. Retrieved 1 December 2011.
  10. ^ Patel, Mona (16 November 2012). "EMC Isilon OneFS 7.0: Converging Big Data and The Enterprise". EMC Big Data Blog. Archived from the original on 12 February 2013. Retrieved 18 January 2013.
  11. ^ Grocott, Sam (30 October 2013). "Isilon OneFS 7.1 Big Data Scale Out Storage Is Finally Here!". EMC Pulse Blog. Retrieved 30 October 2013.
  12. ^ Hughes, Carolyn (8 July 2014). ""Happy launch, @EMCIsilon! 2 fantastic new platforms, flash as cache, new HDFS, and performance galore on OneFS 7.1.1 "Jaws!" Way to go team!"". @carolyn_hugs Twitter. Retrieved 2 September 2014.
  13. ^ "OneFS 7.2.x Release". Dell Inc. 31 October 2014.
  14. ^ Galant, Risa (1 February 2016). "Announcing OneFS 8.0.0".
  15. ^ Noy, David (25 October 2016). "Announcing Isilon OneFS 8.0.1".
  16. ^ Jolley, Todd (21 June 2017). "Dell EMC Announces the Release of Isilon Generation 6 Platform and OneFS 8.1". Dell Inc.
  17. ^ Stevenson, Russ (29 January 2018). "OneFS and Cloudera CDH 5.13+ Support for Cloudera Navigator".
  18. ^ "Isilon OneFS Version 8.1.1 Release Notes" (PDF). Dell Inc. 1 January 2018.
  19. ^ "OneFS 8.1.2 Documentation - Isilon Info Hub". Dell Inc. 3 August 2018.
  20. ^ "OneFS 8.2.0 Release Notes" (PDF). Dell Inc. 3 May 2019.
  21. ^ "OneFS 8.2.1 Release Notes" (PDF). Dell. 6 September 2019.
  22. ^ "OneFS 8.2.2 Release Notes" (PDF). Dell. 16 January 2020.
  23. ^ Mulford, Juan (2020-10-08). "Dell Technologies' PowerScale OneFS 9.1 Released". Storage Review.
  24. ^ a b c d e Trimbee, Nick (January 2023). "Dell PowerScale OneFS: Release Contents". Dell Inc.
  25. ^ "PowerScale OneFS 9.6.x.x. Release Notes". Dell Inc. May 2023.