Date: Sun, 3 Jan 2016 13:20:38 -0600 (CST) From: Bob Friesenhahn <bfriesen@simple.dallas.tx.us> To: "Mikhail T." <mi+thun@aldan.algebra.com> Cc: freebsd-fs@freebsd.org Subject: Re: NFS reads vs. writes Message-ID: <alpine.GSO.2.01.1601031314540.28454@freddy.simplesystems.org> In-Reply-To: <56895E2E.8060405@aldan.algebra.com> References: <568880D3.3010402@aldan.algebra.com> <alpine.GSO.2.01.1601031006020.28454@freddy.simplesystems.org> <56895E2E.8060405@aldan.algebra.com>
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On Sun, 3 Jan 2016, Mikhail T. wrote: > > Why would the same ZFS -- with the same slog -- be working faster, when written to locally, than when over NFS? Yes (it depends). Normal local writes are async writes so they do not use the slog at all. NFS writes are usually synchronous writes so they hit the slog hard. You would need software which intentionally issues synchronous writes to local disks in order to test synchronous local writes. Write sizes of 128k and above are written directly to pool disks and don't go to the slog, even if they are sync writes. This is done to make sure that the slog does not limit pool performance due to bandwidth limitations (vs IOPS). Bob -- Bob Friesenhahn bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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