From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ipmail06.adl6.internode.on.net ([150.101.137.145]:64255 "EHLO ipmail06.adl6.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726687AbeLJVzM (ORCPT ); Mon, 10 Dec 2018 16:55:12 -0500 Date: Tue, 11 Dec 2018 08:55:07 +1100 From: Dave Chinner Subject: Re: RFD: question/probe regarding adding dump-levels A-Z after 0-9 for xfs{dump,restore} Message-ID: <20181210215507.GD6311@dastard> References: <5C0A70FD.6080806@tlinx.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5C0A70FD.6080806@tlinx.org> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: L A Walsh Cc: linux-xfs On Fri, Dec 07, 2018 at 05:09:17AM -0800, L A Walsh wrote: > How difficult would it be to allow 26 more dump levels > in xfs dump/restore? Theoretically anyone using 0-9 > would see no change. Would there be some "problem" or > "gotcha" in adding in what would _seem_ to be a simple > change? Everything _seems_ simple with xfsdump. e.g. the inventory session headers supports up to 255 levels in it's on-disk format, but the xfsdump command is limited to just 10 levels by a separate "max level" define. IOWs, on the surface it _seems_ simple to change it, but I don't know all the places that the dump level is stored, nor what would happen if an older xfsdump/xfsrestore binary tripped over an inventory with a dump level larger than they were compiled to handle. I also don't know if there are scalability problems with resolving the contents of incremental dump levels. Certainly restoring from 30 incremental dumps is more onerous than 6-7, but that's just time. What I don't know is how the invenetory scales to more than 10 incremental and whether there's some exponential algorithm in there that falls apart. So there's a lot of testing that would be needed to validate what looks like a 1 line change to the code. So, yes, technically we could increase the dump level, but there's a *lot* of verification work after doing so and it's not a risk-free modification. FWIW, the idea behind 10 dump levels is that it is enough for a full dump every week w/ an incremental every night of the week until the next full dump is done on the weekend. What's the backup plan you want to use/need that requires a larger number of incrementals? Knowing what you want more dump levels for helps us understand how it would be used and what really needs to be testedi first.... Cheers, Dave. -- Dave Chinner david@fromorbit.com