From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f48.google.com ([209.85.218.48]:34859 "EHLO mail-oi0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756512AbcILRbr (ORCPT ); Mon, 12 Sep 2016 13:31:47 -0400 Received: by mail-oi0-f48.google.com with SMTP id d191so108797243oih.2 for ; Mon, 12 Sep 2016 10:31:47 -0700 (PDT) Subject: Re: Is stability a joke? To: dsterba@suse.cz, Waxhead , linux-btrfs@vger.kernel.org References: <57D51BF9.2010907@online.no> <20160912142714.GE16983@twin.jikos.cz> <52304724-5bca-a1e6-527f-040085c7ab19@gmail.com> <20160912165107.GG16983@twin.jikos.cz> From: "Austin S. Hemmelgarn" Message-ID: <58a954fc-bbd5-3fb5-9f23-008ed7f7121d@gmail.com> Date: Mon, 12 Sep 2016 13:31:42 -0400 MIME-Version: 1.0 In-Reply-To: <20160912165107.GG16983@twin.jikos.cz> Content-Type: text/plain; charset=windows-1252; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 2016-09-12 12:51, David Sterba wrote: > On Mon, Sep 12, 2016 at 10:54:40AM -0400, Austin S. Hemmelgarn wrote: >>> Somebody has put that table on the wiki, so it's a good starting point. >>> I'm not sure we can fit everything into one table, some combinations do >>> not bring new information and we'd need n-dimensional matrix to get the >>> whole picture. >> Agreed, especially because some things are only bad in specific >> circumstances (For example, snapshots generally work fine on almost >> anything, until you get into the range of more than about 250, then they >> start causing issues). > > The performance aspect could be hard to estimate. Each feature has some > cost, we can document what's expected hit but various combinations and > actual runtime performance is unpredictable. I'd rather let the tools do > what the user asks for, as we might not be able to even detect there are > some bad external factors. I think that 250 snapshots would perform > better on an ssd than a rotational disk. In the end this leads to the > "dos & don'ts". > In general yes in this case, but performance starts to degrade exponentially beyond a certain point. The difference between (for example) 10 and 20 snapshots is not as much as between 1000 and 1010. The problem here is that we don't really have a BCP document that anyone ever reads. A lot of stuff that may seem obvious to us after years of working with BTRFS isn't going to be to a newcomer, and it's a lot more likely that some random person will get things write if we have a good, central BCP document than if it stays as scattered tribal knowledge.