Date: Sat, 25 Jan 2014 22:01:53 -0500 From: Garrett Wollman <wollman@bimajority.org> To: Matthew Ahrens <mahrens@delphix.com> Cc: freebsd-fs <freebsd-fs@freebsd.org> Subject: Re: ZFS read performance anomaly / performance regression Message-ID: <21220.31393.533799.991163@hergotha.csail.mit.edu> In-Reply-To: <CAJjvXiHnBq3bg-ZGgyzFw6WBNau0SmoLUfxWLtFCnBwb13fqaQ@mail.gmail.com> References: <21219.21690.165105.561362@hergotha.csail.mit.edu> <CAJjvXiHnBq3bg-ZGgyzFw6WBNau0SmoLUfxWLtFCnBwb13fqaQ@mail.gmail.com>
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<<On Sat, 25 Jan 2014 11:43:28 -0800, Matthew Ahrens <mahrens@delphix.com> said: > How are you reading the files? Could you be reading in less than > block-size chunks (default 128K)? Nope. dd bs=1024k. > This sounds similar to issue discussed in the thread with subject "ZFS slow > reads for unallocated blocks", which was comparing sparse vs cached reads. > Since your storage is so fast, prefetch will probably read and cache the > blocks by the time you issue the read() syscall, so you may be hitting a > similar issue. How would that have changed between 9.1 and 9.2? -GAWollman
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