From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from pepin.polanet.pl ([193.34.52.2]:49097 "EHLO pepin.polanet.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751651AbeA3QW5 (ORCPT ); Tue, 30 Jan 2018 11:22:57 -0500 Date: Tue, 30 Jan 2018 17:22:55 +0100 From: Tomasz Pala To: "Majordomo vger.kernel.org" Subject: Re: degraded permanent mount option Message-ID: <20180130162255.GA28192@polanet.pl> References: <1517035210.1252874.1249880112.19FABD13@webmail.messagingengine.com> <8607255b-98e7-5623-6f62-75d6f7cf23db@gmail.com> <569AC15F-174E-4C78-8FE5-6CE9E0BED479@yayon.me> <111ca301-f631-694d-93eb-b73a790f57d4@gmail.com> <20180127110619.GA10472@polanet.pl> <20180127132641.mhmdhpokqrahgd4n@angband.pl> <20180127224200.GA16927@polanet.pl> <6b6b8e07-27b2-c181-49dc-3fbd1cd9e023@gmail.com> <20180130150950.GB7126@polanet.pl> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-2 In-Reply-To: <20180130150950.GB7126@polanet.pl> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Tue, Jan 30, 2018 at 16:09:50 +0100, Tomasz Pala wrote: >> BCP for over a >> decade has been to put multipathing at the bottom, then crypto, then >> software RAID, than LVM, and then whatever filesystem you're using. > > Really? Let's enumerate some caveats of this: > > - crypto below software RAID means double-encryption (wasted CPU), > > - RAID below LVM means you're stuck with the same RAID-profile for all > the VGs. What if I want 3-way RAID1+0 for crucial data, RAID1 for > system and RAID0 for various system caches (like ccache on software > builder machine) or transient LVM-level snapshots. > > - RAID below filesystem means loosing btrfs-RAID extra functionality, > like recovering data from different mirror when CRC mismatch happens, > > - crypto below LVN means encrypting everything, including data that is > not sensitive - more CPU wasted, And, what is much worse - encrypting everything using the same secret. BIG show-stopper. I would shred such BCP as ineffective and insecure for both, data integrity and confidentiality. > - RAID below LVM means no way to use SSD acceleration of part of the HDD > space using MD write-mostly functionality. -- Tomasz Pala