Good efficiency or good stableness, it''s a question.
Every cow file system a block update will cause update to the block
point to it and recursively to root. Thus these file systems will
write more blocks than in-place update file systems(like ext3). This
cannot be avoided.
But do have some technologies to improve this. NetApp''s WAFL uses
NVRAM-cache to log write operations. Log-structured file systems
always sequentially write to disk to achieve high throughput. BtrFS
uses a B+ tree to limit the height of the tree (so can reduce blocks
need to write in a COW operation), and uses a log tree to speed up
frequently sync operations (I''m not familiar with that).
2009/12/11 Hu Ruihuan <specter118@gmail.com>:> 2009/12/11 Hu Ruihuan <specter118@gmail.com>:
>> Hi all,
>> I am puzzled about a question, everytime when btrfs_writepage is
>> called, whethe the noeds in every levels of the fs tree will be
>> updated. This is the case as I read in the code, but if this case,
>> whether it will give rise to the low efficiency?
>> Thanks!
>>
> refer to the update of nodes, I mean a cow operation
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Zhang Jingwang
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Institute of Computing Technology, Chinese Academy of Sciences
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