Smart File System: Difference between revisions

Revision as of 00:29, 15 June 2017

Revision as of 10:50, 4 September 2017

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== Features ==

SFS uses block sizes ranging from 512 (2⁹) to 32768 (2¹⁵) [[byte]]s with a maximum partition size of 128 GB.

Its good performance, better than [[Amiga Fast File System|FFS]], and lack of need for long "validation" in case of an error,<ref name="Hyperion">{{cite web|url=http://blog.hyperion-entertainment.biz/?p=210|title=Hard drive setup for AmigaOS 4.1 Classic|website=[[Hyperion Entertainment]] Blog|author=Darren Eveland}}</ref><ref name="TotalAmiga">{{cite journal|work=Total Amiga|url=http://www.totalamiga.org/pdf/totalamiga_6.pdf|title=Hard Drivin'|page=45|author=Robert Williams|issue=6|year=2000}}</ref> is achieved by grouping multiple directory entries into a single block and by grouping meta data blocks together into clusters.<ref name="Forensics">{{cite book |author=EC-Council |title=Computer Forensics: Investigating Hard Disks, File and Operating Systems |date= 2009 |publisher=Cengage Learning |isbn=1-4354-8350-2 |pagepages=1-161–16 |chapter=Understanding File Systems and Hard Disks |url=http://news.asis.io/sites/default/files/Investigating_Hard_Disks_File__Operating_Systems.pdf }}</ref> A [[free space bitmap|bitmap]] is used to keep track of free space, and file data is kept track of using extents arranged into a [[B+ tree]] structure.<ref name="Forensics" />

Integrity is maintained by keeping a [[transaction log]] of all changes made to metadata over a certain period of time.<ref name="Forensics" /> The log is written to disk first into free space and then meta data blocks are overwritten directly. Should the system crash, the next time the filesystem is mounted it will notice the uncompleted operation and roll it back to the last known consistent state. For performance reasons, only metadata integrity is ensured. Actual data in files can still be corrupted if a write operation is terminated half wayhalfway through.<ref>{{cite web |url=http://www.amiga-stuff.com/text/filesystems/SFS.guide |author=Hendrikx, J |title=Smart Filesystem documentation |date=4 August 1998 |archive-url=https://web.archive.org/web/20040707174441/http://www.amiga-stuff.com/text/filesystems/SFS.guide |archivedate=2004-07-07 }}</ref> Unlike the original Amiga filesystems, [[Amiga Fast File System|FFS]] and [[Amiga Old File System|OFS]], filesystem integrity is very rarely compromised by this.

One feature of SFS that is almost unique among Amiga filesystems is its ability to [[defragmentation|defragment]] itself while the filesystem is in use, even for locked files.<ref name="Forensics" /> The defragmentation process is almost completely stateless (apart from the ___location it is working on), which means it can be stopped and started instantly. During defragmentation data integrity is ensured of both meta data and normal data. The filesystem may attempt to move a whole file to a different ___location when fragmentation is going to occur otherwise.<ref name="Forensics2">{{cite book|author1=Husrev Taha Sencar|author2=[[Nasir Memon]]|title=Digital Image Forensics: There is More to a Picture than Meets the Eye|url=https://books.google.com/books?id=PzP9ViF8oAIC&pg=PA130 |date=1 August 2012|publisher=Springer Science & Business Media|isbn=978-1-4614-0757-7|page=130}}</ref>

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{{asof|2008}}, SFS was one of the independent filesystems still being used on Amiga computers.<ref>{{cite web|website=[[Ars Technica]]|url=https://arstechnica.com/gadgets/2008/03/past-present-future-file-systems/4/|title=From BFS to ZFS: past, present and future of file systems|author=Jeremy Reimer|publisher=[[Condé Nast Publications]]|date=18 March 2008|quote=Many people did that, and some of the results, such as the Professional File System (PFS) and Smart File System (SFS), are still used by Amiga fans to this day.}}</ref>

Versions for AROS, AmigaOS and MorphOS are based on different branches. The Linux version is independent code.{{cncitation needed|date=October 2015}}

== See also ==