Need hint for my question regarding the working of rsync.

[Kevin Korb]

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Is there a hard links limit?  I have been in the 70-80 million range
on ext4 without a problem (other than performance which is why I
switched to ZFS for that use case).

On 11/13/13 13:59, Karl O. Pinc wrote:
> On 11/13/2013 12:03:21 PM, Kevin Korb wrote:
>> OK, in the case of using v3 with --link-dest and not --checksum
>> most of the initial activity on the sender would be doing calls
>> to stat() to index what is there.
>> 
>> The receiving side would be doing 2x the stat() calls (you have
>> 2 --link-dest dirs for it to check) and link() calls every time
>> it finds a matching file.
> 
> Am I correct in my impression that the sender and receiver are
> doing the above serially, not concurrently?
> 
>> stat() is an expensive call in terms of time spent (especially
>> when multiplied by millions of files) but it doesn't really
>> translate into much disk IO since it is such a small amount of
>> actual data.  The link() call is pretty much the same except it
>> is a write op instead of a read op.  So, you wouldn't show much
>> MB/sec usage of your disks until rsync found a new or different
>> file but there would be many small operations.
> 
> My thought is to save wall time by increasing concurrency.
> 
> No doubt there are tradeoffs involved.  If forced to choose between
> features what I really want is entirely different; for -H to have
> "priority" over --link-dest so that when the fs surpasses its
> hardlink limit the end result is that the -H links exist and the
> --link-dest links do not.  Future --link-dest operations would then
> work and, most importantly, the result of the running rsync
> operation would be a good copy of the source.  This would allow 
> many --link-dest-ed backups of a fs used by hardlink-happy
> applications.  (Like yum.)
> 
> 
> Karl <kop at meme.com> Free Software:  "You don't pay back, you pay
> forward." -- Robert A. Heinlein
> 

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