From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp-16-i2.italiaonline.it ([212.48.25.194]:49678 "EHLO smtp-16.italiaonline.it" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751164AbaLHOdK (ORCPT ); Mon, 8 Dec 2014 09:33:10 -0500 Message-ID: <5485B6EB.1030101@inwind.it> Date: Mon, 08 Dec 2014 15:34:19 +0100 From: Goffredo Baroncelli Reply-To: kreijack@inwind.it MIME-Version: 1.0 To: ashford@whisperpc.com CC: Shriramana Sharma , Martin Steigerwald , linux-btrfs Subject: Re: Why is the actual disk usage of btrfs considered unknowable? References: <44320137.fRRuR6EFMP@merkaba> <5484A83A.5090109@inwind.it> <6554b2b132dd3f9803bcf8c10f11a156.squirrel@webmail.wanet.net> <5484DC3C.7040409@inwind.it> <73b1fa42cc61f5a843206a8164952f74.squirrel@webmail.wanet.net> In-Reply-To: <73b1fa42cc61f5a843206a8164952f74.squirrel@webmail.wanet.net> Content-Type: text/plain; charset=windows-1252 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 12/08/2014 01:12 AM, ashford@whisperpc.com wrote: > Goffredo, > >> So in case you have a raid1 filesystem on two disks; each disk has 300GB >> free; which is the free space that you expected: 300GB or 600GB and why ? > > You should see 300GB free. That's what you'll see with RAID-1 with a > hardware RAID controller, and with MD RAID. Why would you expect to see > anything else with BTRFS RAID? I had to ask you because in a your previous email you stated something different: On 12/07/2014 09:32 PM, ashford@whisperpc.com wrote: > I disagree. My experiences with other file-systems, including ZFS, show > that the most common solution is to just deliver to the user the actual > amount of *unused disk space* ^^^^^^^^^^^^^^^^^^^ So I expected that you answered with 600GB. But you have told the true: the user want to know how many data is able to store on the disk, and not the unused disk space. But I have to point out that the common case is one disk filesystem where the metadata chunks have a ratio data stored/disk space consumed of 1:2; the data chunks have a ratio of 1:1. This is one reason why is difficult to evaluate the free space: if you have all metadata chunks, you have to half the disk space. Another reason is that there is the idea to allow different raid profiles in the same filesystem. This will further complicate the free space evaluation. > Peter Ashford G.Baroncelli > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- gpg @keyserver.linux.it: Goffredo Baroncelli Key fingerprint BBF5 1610 0B64 DAC6 5F7D 17B2 0EDA 9B37 8B82 E0B5