On 10-Apr-09, at 2:03 PM, Harry Putnam wrote:
David Magda <dma...@ee.ryerson.ca> writes:
On Apr 7, 2009, at 16:43, OpenSolaris Forums wrote:
if you have a snapshot of your files and rsync the same files again,
you need to use "--inplace" rsync option , otherwise completely new
blocks will be allocated for the new files. that`s because rsync
will write entirely new file and rename it over the old one.
not sure if this applies here, but i think it`s worth mentioning and
not obvious.....
With ZFS new blocks will always be allocated: it's copy-on-write
(COW)
file system.
So who is right here...
As far as I can see - the effect of --inplace would be that new
blocks are allocated for the deltas, not the whole file, so Daniel
Rock's finding does not contradict "OpenSolaris Forums". But in
either case, COW is involved.
--Toby
Daniel Rock says he can see on disk that it
doesn't work that way... that is only a small amount of space is taken
when rsyncing in this way.
See his post:
From: Daniel Rock <sola...@deadcafe.de>
Subject: Re: Data size grew.. with compression on
Newsgroups: gmane.os.solaris.opensolaris.zfs
To: zfs-discuss@opensolaris.org
Date: Thu, 09 Apr 2009 16:35:07 +0200
Message-ID: <49de079b.2040...@deadcafe.de>
[...]
Johnathon wrote:
ZFS will allocate new blocks either way
Daniel R replied: No it won't. --inplace doesn't rewrite blocks
identical on source and target but only blocks which have been
changed.
I use rsync to synchronize a directory with a few large files (each
up to 32 GB). Data normally gets appended to one file until it
reaches the size limit of 32 GB. Before I used --inplace a snapshot
needed on average ~16 GB. Now with --inplace it is just a few
kBytes.
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