Re: Does nilfs2 do any in-place writes?

[Vyacheslav Dubeyko <slava-yeENwD64cLxBDgjK7y7TUQ@public.gmane.org>]

Hi Clemens,

On Wed, 2014-01-15 at 12:44 +0100, Clemens Eisserer wrote:
> Hi Vyacheslav,
> 
> > The main approach of NILFS2 is COW (copy-on-write) policy. It means that
> > all data and metadata are written in log manner. Only superblocks are
> > placed in fixed positions and updated there. First superblock is located
> > in the volume begin, second one in the volume end.
> 
> Can you give me an estime how often the superblock is updated / written to?
> 

NILFS2 has special method nilfs_sb_need_update() [1] and special
constant NILFS_SB_FREQ [2] that it is used usually for definition
frequency of superblocks updating. So, as far as I can judge, default
value of such frequency under high I/O load is 10 seconds (Minimum
interval of periodical update of superblocks (in seconds)).

With the best regards,
Vyacheslav Dubeyko.

[1] http://lxr.free-electrons.com/source/fs/nilfs2/the_nilfs.h#L254
[2] http://lxr.free-electrons.com/source/fs/nilfs2/the_nilfs.h#L252


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