Re: [zfs-discuss] article on btrfs, comparison with zfs
Roch wrote: I don't know what 'enters the txg' exactly is but ZFS disk-block allocation is done in the ZIO pipeline at the latest possible time. Thanks Roch, I stand corrected in my assumptions. Cheers, Henk ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] article on btrfs, comparison with zfs
Henk Langeveld writes: > Mario Goebbels wrote: > >>> An introduction to btrfs, from somebody who used to work on ZFS: > >>> > >>> http://www.osnews.com/story/21920/A_Short_History_of_btrfs > >> *very* interesting article.. Not sure why James didn't directly link to > >> it, but courteous of Valerie Aurora (formerly Henson) > >> > >> http://lwn.net/Articles/342892/ > > > > I'm trying to understand the argument against the SLAB allocator > > approach. If I understood correctly how BTRFS allocates space, changing > > and deleting files may just punch randomly sized holes into the disk > > layout. How's that better? > > It's an interesting article, for sure. The core of the article is actually > how a solution (b+trees with copy-on-write) found a problem (file systems). > > To answer the question, the article claims that reallocation is part of the > normal process writing data: > > > Defragmentation is an ongoing process - repacking the items > > efficiently is part of the normal code path preparing extents to be > > written to disk. Doing checksums, reference counting, and other > > assorted metadata busy-work on a per-extent basis reduces overhead > > and makes new features (such as fast reverse mapping from an extent > > to everything that references it) possible. > > It sure suggests what is happening, but I haven't got a clue on how the above > makes a difference. Translating this to the ZFS design, I guess it involves > delaying the block layout to the actual txg i/o phase, while zfs already > decides this when a block enters the txg, it's layout has been decided > already. > Henk, I don't know what 'enters the txg' exactly is but ZFS disk-block allocation is done in the ZIO pipeline at the latest possible time. > This allows for blocks to be dumped into a slog device as soon as it is > available. > I'm not sure what this refers to. -r > Cheers, > Henk > ___ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] article on btrfs, comparison with zfs
"C. Bergström" writes: > James C. McPherson wrote: > > An introduction to btrfs, from somebody who used to work on ZFS: > > > > http://www.osnews.com/story/21920/A_Short_History_of_btrfs > > > *very* interesting article.. Not sure why James didn't directly link to > it, but courteous of Valerie Aurora (formerly Henson) > > http://lwn.net/Articles/342892/ > > In terms of the ZFS comparison, Valerie gets it wrong. ZFS allocates out of metaslabs and space maps which take arbitrary size as an argument : http://src.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/fs/zfs/metaslab.c#388 Further reading : http://blogs.sun.com/bonwick/entry/space_maps -r > > > ___ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] article on btrfs, comparison with zfs
Mario Goebbels wrote: An introduction to btrfs, from somebody who used to work on ZFS: http://www.osnews.com/story/21920/A_Short_History_of_btrfs *very* interesting article.. Not sure why James didn't directly link to it, but courteous of Valerie Aurora (formerly Henson) http://lwn.net/Articles/342892/ I'm trying to understand the argument against the SLAB allocator approach. If I understood correctly how BTRFS allocates space, changing and deleting files may just punch randomly sized holes into the disk layout. How's that better? It's an interesting article, for sure. The core of the article is actually how a solution (b+trees with copy-on-write) found a problem (file systems). To answer the question, the article claims that reallocation is part of the normal process writing data: > Defragmentation is an ongoing process - repacking the items > efficiently is part of the normal code path preparing extents to be > written to disk. Doing checksums, reference counting, and other > assorted metadata busy-work on a per-extent basis reduces overhead > and makes new features (such as fast reverse mapping from an extent > to everything that references it) possible. It sure suggests what is happening, but I haven't got a clue on how the above makes a difference. Translating this to the ZFS design, I guess it involves delaying the block layout to the actual txg i/o phase, while zfs already decides this when a block enters the txg, it's layout has been decided already. This allows for blocks to be dumped into a slog device as soon as it is available. Cheers, Henk ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] article on btrfs, comparison with zfs
An introduction to btrfs, from somebody who used to work on ZFS: http://www.osnews.com/story/21920/A_Short_History_of_btrfs *very* interesting article.. Not sure why James didn't directly link to it, but courteous of Valerie Aurora (formerly Henson) http://lwn.net/Articles/342892/ I'm trying to understand the argument against the SLAB allocator approach. If I understood correctly how BTRFS allocates space, changing and deleting files may just punch randomly sized holes into the disk layout. How's that better? Regards, -mg ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] article on btrfs, comparison with zfs
James C. McPherson wrote: An introduction to btrfs, from somebody who used to work on ZFS: http://www.osnews.com/story/21920/A_Short_History_of_btrfs *very* interesting article.. Not sure why James didn't directly link to it, but courteous of Valerie Aurora (formerly Henson) http://lwn.net/Articles/342892/ ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
[zfs-discuss] article on btrfs, comparison with zfs
An introduction to btrfs, from somebody who used to work on ZFS: http://www.osnews.com/story/21920/A_Short_History_of_btrfs James C. McPherson -- Senior Kernel Software Engineer, Solaris Sun Microsystems http://blogs.sun.com/jmcp http://www.jmcp.homeunix.com/blog Kernel Conference Australia - http://au.sun.com/sunnews/events/2009/kernel ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
