From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f49.google.com ([74.125.82.49]:36169 "EHLO mail-wm0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755645AbcBIOHF (ORCPT ); Tue, 9 Feb 2016 09:07:05 -0500 Received: by mail-wm0-f49.google.com with SMTP id p63so159675629wmp.1 for ; Tue, 09 Feb 2016 06:07:05 -0800 (PST) Subject: Re: BTRFS RAM requirements, RAID 6 stability/write holes and expansion questions To: Mackenzie Meyer , linux-btrfs@vger.kernel.org References: From: Psalle Message-ID: <56B9F286.9070408@gmail.com> Date: Tue, 9 Feb 2016 15:07:02 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 05/02/16 20:36, Mackenzie Meyer wrote: > Hello, > > I've tried checking around on google but can't find information > regarding the RAM requirements of BTRFS and most of the topics on > stability seem quite old. To keep my answer short: every time I've tried (offline) deduplication or raid5 pools I've ended with borked filesystems. Last attempt was about a year ago. Given that the pages you mention looked the same by then, I'd stay away of raid56 for anything but testing purposes. I haven't read anything about raid5 that increases my confidence in it recently (i.e. post 3.19 kernels). Dedup, OTOH, I don't know. What I used were third-party (I think?) things so the fault may have rested on them and not btrfs (does that makes sense?) I'm building a new small raid5 pool as we speak, though, for throw-away data, so I hope to be favourably impressed. Cheers. > So first would be memory requirements, my goal is to use deduplication > and compression. Approximately how many GB of RAM per TB of storage > would be recommended? > > RAID 6 write holes? > The BTRFS wiki states that parity might be inconsistent after a crash. > That said, the wiki page for RAID 5/6 doesn't look like it has much > recent information on there. Has this issue been addressed and if not, > are there plans to address the RAID write hole issue? What would be a > recommended workaround to resolve inconsistent parity, should an > unexpected power down happen during write operations? > > RAID 6 stability? > Any articles I've tried looking for online seem to be from early 2014, > I can't find anything recent discussing the stability of RAID 5 or 6. > Are there or have there recently been any data corruption bugs which > impact RAID 6? Would you consider RAID 6 safe/stable enough for > production use? > > Do you still strongly recommend backups, or has stability reached a > point where backups aren't as critical? I'm thinking from a data > consistency standpoint, not a hardware failure standpoint. > > I plan to start with a small array and add disks over time. That said, > currently I have mostly 2TB disks and some 3TB disks. If I replace all > 2TB disks with 3TB disks, would BTRFS then start utilizing the full > 3TB capacity of each disk, or would I need to destroy and rebuild my > array to benefit from the larger disks? > > > Thanks! > -- > 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