Need hint for my question regarding the working of rsync.
kmk at sanitarium.net
Wed Nov 13 12:04:29 MST 2013
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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
Kevin Korb Phone: (407) 252-6853
Systems Administrator Internet:
FutureQuest, Inc. Kevin at FutureQuest.net (work)
Orlando, Florida kmk at sanitarium.net (personal)
Web page: http://www.sanitarium.net/
PGP public key available on web site.
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