From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: Time to deprecate old RAID formats? Date: Wed, 24 Oct 2007 20:09:21 -0400 Message-ID: <471FDEB1.8040401@garzik.org> References: <18200.49267.763509.924873@stoffel.org> <18200.53593.687483.120827@stoffel.org> <1192810534.1666.68.camel@firewall.xsintricity.com> <18200.56684.14194.630264@stoffel.org> <1192813877.1666.79.camel@firewall.xsintricity.com> <18200.63987.514073.184865@stoffel.org> <471E7DC6.7050206@tmr.com> <1193184555.10336.3.camel@firewall.xsintricity.com> <18207.56169.769976.512617@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <18207.56169.769976.512617@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: Neil Brown Cc: Doug Ledford , Bill Davidsen , John Stoffel , Justin Piszcz , linux-raid@vger.kernel.org List-Id: linux-raid.ids Neil Brown wrote: > On Tuesday October 23, dledford@redhat.com wrote: > As for where the metadata "should" be placed, it is interesting to > observe that the SNIA's "DDFv1.2" puts it at the end of the device. > And as DDF is an industry standard sponsored by multiple companies it > must be ...... > Sorry. I had intended to say "correct", but when it came to it, my > fingers refused to type that word in that context. > > DDF is in a somewhat different situation though. It assumes that the > components are whole devices, and that the controller has exclusive > access - there is no way another controller could interpret the > devices differently before the DDF controller has a chance. agreed. > DDF is also interesting in that it uses 512 byte alignment for > metadata. The 'anchor' block is in the last sector of the device. > This contrasts with current md metadata which is all 4K aligned. > Given that the drive manufacturers seem to be telling us that "4096 is > the new 512", I think 4K alignment was a good idea. > It could be that DDF actually specifies the anchor to reside in the > last "block" rather than the last "sector", and it could be that the > spec allows for block size to be device specific - I'd have to hunt > through the spec again to be sure. Its a bit of a mess. Yes, with 1K and 4K sector devices starting to appear, as long as the underlying partitioning gets the initial partition alignment correct, this /should/ continue functioning as normal. If for whatever reason you wind up with an odd-aligned 1K sector device and your data winds up aligned to even numbered [hard] sectors, performance will definitely suffer. Mostly this is out of MD's hands, and up to the sysadmin and partitioning tools to get hard-sector alignment right. > For the record, I have no intention of deprecating any of the metadata > formats, not even 0.90. strongly agreed > It is conceivable that I could change the default, though that would > require a decision as to what the new default would be. I think it > would have to be 1.0 or it would cause too much confusion. A newer default would be nice. Jeff