From mboxrd@z Thu Jan 1 00:00:00 1970 From: Phil Turmel Subject: Re: Linux Plumbers MD BOF discussion notes Date: Wed, 4 Oct 2017 17:18:09 -0400 Message-ID: <5716615d-ae85-8822-0c21-da4e85dcff00@turmel.org> References: <20170915142737.qafwl3vgl6vhfi5q@kernel.org> <871sn78pzt.fsf@notabene.neil.brown.name> <874ls0s7un.fsf@notabene.neil.brown.name> <87lgkr3fgj.fsf@notabene.neil.brown.name> <619758c0-9ca4-c25d-c61b-f411b095041d@intel.com> <076977d4-dfae-e8d3-7606-29e838f422ec@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <076977d4-dfae-e8d3-7606-29e838f422ec@intel.com> Content-Language: en-GB Sender: linux-raid-owner@vger.kernel.org To: Artur Paszkiewicz , NeilBrown , Mikael Abrahamsson Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 10/04/2017 07:23 AM, Artur Paszkiewicz wrote: > On 10/04/2017 01:02 PM, Artur Paszkiewicz wrote: >> Applications like mdadm can use this to hide/unhide their component >> devices. > > And here is an example patch for mdadm. It adds options to manually hide > or unhide the component devices: > > mdadm --hide-components /dev/md0 > mdadm --unhide-components /dev/md0 > > And an option for mdadm.conf that automatically hides the array's member > disks when assembling and when new disks are added: > > ARRAY /dev/md/0 metadata=1.2 UUID=c2c4f8c6:cd775924:9cb2cc62:88fa45bd > name=linux-ns31:0 hide-components=yes > > Hidden disks (by mdadm --hide-components or by config) should unhide > when the array is stopped or disks are removed. It only works for whole > devices, not partitions. I am not at all in favor of these patches, as they break all kinds of diagnostic tooling and certainly violate the principle of least surprise. Tools like "lsblk --tree" and my own "lsdrv" [1]. Please keep these out of the kernel, or better yet, explain to your customers that visibility into the components is a key *advantage* of software raid. Regards, Phil Turmel [1] https://github.com/pturmel/lsdrv