Date: Sun, 13 Nov 2022 11:46:42 -0600 (CST) From: Bob Friesenhahn <bfriesen@simple.dallas.tx.us> To: Mark Saad <nonesuch@longcount.org> Cc: freebsd-fs@FreeBSD.org Subject: Re: Odd behaviour of two identical ZFS servers mirroring via rsync Message-ID: <alpine.GSO.2.20.2211131137020.7126@scrappy.simplesystems.org> In-Reply-To: <CAMXt9Nbr=7K6PELVGAPZ=-RiAfx=zp9iOoKyWdH=0H2=AiE52Q@mail.gmail.com> References: <alpine.BSF.2.22.395.2211111709230.29479@mail0.time-domain.net> <CAOgwaMuoLQ9Er67Y%2B=q%2Bf9724v2WT3L5v5TZaRVXq%2B=1vEyJ%2BA@mail.gmail.com> <alpine.BSF.2.22.395.2211112008220.30520@mail0.time-domain.net> <alpine.GSO.2.20.2211121949060.7126@scrappy.simplesystems.org> <CAMXt9Nbr=7K6PELVGAPZ=-RiAfx=zp9iOoKyWdH=0H2=AiE52Q@mail.gmail.com>
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On Sun, 13 Nov 2022, Mark Saad wrote:
>>
> Bob are you saying when the target is zfs --inplace --no-whole-file helps
> or just in general when you have
> large files ? Also have you tried using --delete-during / --delete-after ?
The '-inplace --no-whole-file' updates the file blocks if they have
changed (comparing the orgin blocks with the existing mirror blocks)
rather than creating a new copy of the file and moving it into place
when it is complete. ZFS does not check if data content has been
changed while it is being written so a write of the same data will
result in a fresh allocation based on its Copy On Write ("COW")
design. Writing a whole new file obviously significantly increases
the number of blocks which are written. Requesting that rsync only
write to the file for the blocks which have changed reduces the total
number of blocks which get written.
The above helps quite a lot when using snapshots since then fewer
blocks are in the snapshots.
I have never tried --delete-during so I can't comment on that.
Bob
--
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
Public Key, http://www.simplesystems.org/users/bfriesen/public-key.txt
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