From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f66.google.com ([209.85.214.66]:39729 "EHLO mail-it0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388110AbeGTTgR (ORCPT ); Fri, 20 Jul 2018 15:36:17 -0400 Received: by mail-it0-f66.google.com with SMTP id g141-v6so13476019ita.4 for ; Fri, 20 Jul 2018 11:46:45 -0700 (PDT) Subject: Re: [PATCH 0/4] 3- and 4- copy RAID1 To: Hugo Mills , Andrei Borzenkov , kreijack@inwind.it, Duncan <1i5t5.duncan@cox.net>, linux-btrfs@vger.kernel.org References: <9945d460-99b5-a927-a614-c797bbc7862d@dirtcellar.net> <793d8ec3-7934-ea60-521d-7a039c9f1ce9@libero.it> <89d20da9-0e80-51d1-3a4f-4cccb44d31ef@libero.it> <2f1b19da-f2a2-077b-eee1-1106f40679ac@gmail.com> <1066d34f-2703-19e3-62ea-c4178640b8c3@gmail.com> <20180720184159.GD21293@carfax.org.uk> From: "Austin S. Hemmelgarn" Message-ID: Date: Fri, 20 Jul 2018 14:46:42 -0400 MIME-Version: 1.0 In-Reply-To: <20180720184159.GD21293@carfax.org.uk> Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 2018-07-20 14:41, Hugo Mills wrote: > On Fri, Jul 20, 2018 at 09:38:14PM +0300, Andrei Borzenkov wrote: >> 20.07.2018 20:16, Goffredo Baroncelli пишет: > [snip] >>> Limiting the number of disk per raid, in BTRFS would be quite simple to implement in the "chunk allocator" >>> >> >> You mean that currently RAID5 stripe size is equal to number of disks? >> Well, I suppose nobody is using btrfs with disk pools of two or three >> digits size. > > But they are (even if not very many of them) -- we've seen at least > one person with something like 40 or 50 devices in the array. They'd > definitely got into /dev/sdac territory. I don't recall what RAID level > they were using. I think it was either RAID-1 or -10. > > That's the largest I can recall seeing mention of, though. I've talked to at least two people using it on 100+ disks in a SAN situation. In both cases however, BTRFS itself was only seeing about 20 devices and running in raid0 mode on them, with each of those being a RAID6 volume configured on the SAN node holding the disks for it. From what I understood when talking to them, they actually got rather good performance in this setup, though maintenance was a bit of a pain.