Date: Mon, 6 Dec 2010 21:31:39 +0100 From: Ivan Voras <ivoras@freebsd.org> To: John Baldwin <jhb@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Pawel Jakub Dawidek <pjd@freebsd.org> Subject: Re: svn commit: r216230 - head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs Message-ID: <AANLkTi=Bnkq8sR3j7kq-aKzbk0TEd=kFiyr%2BqeQpzXGc@mail.gmail.com> In-Reply-To: <201012061518.49835.jhb@freebsd.org> References: <201012061218.oB6CI3oW032770@svn.freebsd.org> <AANLkTine9rGq_cM4ruFXYq=-F7cMXcQAr-zKHuWoQs2z@mail.gmail.com> <20101206195327.GD1936@garage.freebsd.pl> <201012061518.49835.jhb@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On 6 December 2010 21:18, John Baldwin <jhb@freebsd.org> wrote: > On Monday, December 06, 2010 2:53:27 pm Pawel Jakub Dawidek wrote: >> On Mon, Dec 06, 2010 at 08:35:36PM +0100, Ivan Voras wrote: >> > Please persuade me on technical grounds why ashift, a property >> > intended for address alignment, should not be set in this way. If your >> > answer is "I don't know but you are still wrong because I say so" I >> > will respect it and back it out but only until I/we discuss the >> > question with upstream ZFS developers. >> >> No. You persuade me why changing ashift in ZFS, which, as the comment >> clearly states is "device's minimum transfer size" is better and not >> hackish than presenting the disk with properly configured sector size. >> This can not only affect disks that still use 512 bytes sectors, but >> doesn't fix the problem at all. It just works around the problem in ZFS >> when configured on top of raw disks. >> >> What about other file systems? What about other GEOM classes? GELI is >> great example here, as people use ZFS on top of GELI alot. GELI >> integrity verification works in a way that not reporting disk sector >> size properly will have huge negative performance impact. ZFS' ashift >> won't change that. > > I am mostly on your side here, but I wonder if GELI shouldn't prefer the > stripesize anyway? =C2=A0For example, if you ran GELI on top of RAID-5 I = imagine it > would be far more performant for it to use stripe-size logical blocks ins= tead > of individual sectors for the underlying media. > > The RAID-5 argument also suggests that other filesystems should probably > prefer stripe sizes to physical sector sizes when picking block sizes, et= c. For what it's worth, apparently linux has the concept of "physical" and "logical" sector sizes (possibly in addition to "stripe size"), with physical being 4096 and logical 512, for example: # hdparm -I /dev/sde | grep size Logical Sector size: 512 bytes Physical Sector size: 4096 bytes device size with M =3D 1024*1024: 1430799 MBytes device size with M =3D 1000*1000: 1500301 MBytes (1500 GB)
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?AANLkTi=Bnkq8sR3j7kq-aKzbk0TEd=kFiyr%2BqeQpzXGc>