Date: Thu, 11 Apr 2013 19:08:36 +0200 From: Adam Nowacki <nowakpl@platinum.linux.pl> To: freebsd-fs@freebsd.org Subject: Re: ZFS slow reads for unallocated blocks Message-ID: <5166EE14.1090806@platinum.linux.pl> In-Reply-To: <5166ECBA.1090005@gmail.com> References: <5166EA43.7050700@platinum.linux.pl> <5166ECBA.1090005@gmail.com>
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On 2013-04-11 19:02, Chuck Burns wrote: > On 4/11/2013 11:52 AM, Adam Nowacki wrote: >> This one is quite weird - reads from files that were created and resized >> with ftruncate (so no actual data on disk) are considerably slower and >> use more CPU time than files with data. If compression is enabled this >> will also affect files with long runs of zeroes as ZFS won't write any >> data to disk in this case. There is no I/O on the pool during the read >> tests - all fits into 10GB ARC. >> >> FreeBSD storage 9.1-RELEASE FreeBSD 9.1-RELEASE #0: Sat Feb 23 15:51:26 >> UTC 2013 root@storage:/usr/obj/usr/src/sys/GENERIC amd64 > <snip> > > Sounds like it could be a CPU bottleneck? How about some cpu info? > > hw.model: AMD FX(tm)-4100 Quad-Core Processor hw.ncpu: 4 But this doesn't matter much as CPU time should be compared relative to other tests - 1 second versus 15 seconds on the same CPU.
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