From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shaohua Li Subject: Re: RAID creation resync behaviors Date: Wed, 10 May 2017 10:30:29 -0700 Message-ID: <20170510173029.7cumdgokh6viebgq@kernel.org> References: <20170503202748.7r243wj5h4polt6y@kernel.org> <87inlhpgzu.fsf@notabene.neil.brown.name> <20170504020452.kcmjgxnk7zsx7kdx@kernel.org> <1fca5ff4-358a-e0cf-d1a4-fc33ecdcbd62@gmail.com> <87o9v1n56m.fsf@notabene.neil.brown.name> <76407cb7-437b-142e-e74b-ddd56f3f4ddb@gmail.com> <08ba08b3-0e8c-c064-6b35-9084545e2c22@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Jes Sorensen Cc: "Martin K. Petersen" , NeilBrown , linux-raid@vger.kernel.org, neilb@suse.de List-Id: linux-raid.ids On Tue, May 09, 2017 at 05:22:57PM -0400, Jes Sorensen wrote: > On 05/09/2017 05:16 PM, Martin K. Petersen wrote: > > > > Jes, > > > > > This is fine within the kernel, however it is not overly useful for > > > mdadm to determine which strategy to apply when syncing devices. > > > > BLKZEROOUT > > > > Trying to read the code, as this ioctl doesn't seem to be documented > anywhere I can find.... it looks like this ioctl zeroes out a device. > > It doesn't help me obtain the information I need to make a decision in mdadm > as whether to overwrite all or compare+write when resyncing a RAID array. The best way I can think is if we find the disks are SSD, trim the disks, and read some random places. If all return 0, the guess is the SSD returns 0 after trim, so do compare-write resync otherwise overwrite. Surely this needs extra mdadm option to enable. We can only reliably detect a SSD, others lie. Thanks, Shaohua