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? For 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 instead 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, etc. -- John Baldwin _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
