OT: Wikipedia FS comparsion page needs update

Matthew Dillon dillon at apollo.backplane.com
Sun May 23 09:34:15 PDT 2010

:Hell Low.
:I think we should conduct a slight PR move
:and update [1] w.r.t HAMMER.

    Well, if someone wants to correct it, sure.  I haven't made any
    edits to wikipedia in a long time so it generally doesn't let me
    edit without creating a hassle.

:What can be said about data layout?
:The table at [1] has following columns:
:? Block suballocation
:? Variable file block size
:? Extents

    Each block is indexed via the B-Tree. The block size is variable but
    the current implementation limits itself to 16K and 64K block sizes.
    Extents are theoretically doable but the current implementation
    does not use extents.

:? Allocate-on-flush

    Hybrid allocation model.  Reserve on write, allocate on flush.

:+ Sparse files


:- Transparent compression


:What are those limitations for HAMMER?
:? Maximum filename length

    255 chars.

:? Allowable characters in directory entries (are there exceptions?)

    No limitations except for '/' of course.

:? Maximum pathname length

    Limited by the OS (typically 1024).

:? Maximum file size

    Approximately 2^63 bytes

:Does it support ACLs, Security/MAC labels,
:extended attributes, alternate data streams, forks?


:What can be said about CoW, Block journaling or
:Metadata-only journaling of HAMMER?
:Can something be said w.r.t XIP [2]?

    Infinite fine-grained automatic snapshots.

:I guess HAMMER volume still cannot be shrunk,
:nor can it deduplicate.

    No, though dedup is easy to do.  There were no takers on the dedup
    GSOC project though.

					Matthew Dillon 
					<dillon at backplane.com>

:[1] http://en.wikipedia.org/wiki/Comparison_of_file_systems
:[2] http://en.wikipedia.org/wiki/Execute_in_place
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