From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lists.gentoo.org (pigeon.gentoo.org [208.92.234.80]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by finch.gentoo.org (Postfix) with ESMTPS id A4A4E158020 for ; Wed, 21 Dec 2022 20:03:44 +0000 (UTC) Received: from pigeon.gentoo.org (localhost [127.0.0.1]) by pigeon.gentoo.org (Postfix) with SMTP id 16F78E086C; Wed, 21 Dec 2022 20:03:39 +0000 (UTC) Received: from smtp.hosts.co.uk (smtp.hosts.co.uk [85.233.160.19]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by pigeon.gentoo.org (Postfix) with ESMTPS id C2214E0824 for ; Wed, 21 Dec 2022 20:03:38 +0000 (UTC) Received: from host86-138-24-20.range86-138.btcentralplus.com ([86.138.24.20] helo=[192.168.1.65]) by smtp.hosts.co.uk with esmtpa (Exim) (envelope-from ) id 1p85JQ-0009Uw-53 for gentoo-user@lists.gentoo.org; Wed, 21 Dec 2022 20:03:36 +0000 Message-ID: <49c8e857-0ed9-0dfd-341b-af955635337c@youngman.org.uk> Date: Wed, 21 Dec 2022 20:03:36 +0000 Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-Id: Gentoo Linux mail X-BeenThere: gentoo-user@lists.gentoo.org Reply-to: gentoo-user@lists.gentoo.org X-Auto-Response-Suppress: DR, RN, NRN, OOF, AutoReply MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [gentoo-user] NAS and replacing with larger drives To: gentoo-user@lists.gentoo.org References: <9407e524-2226-6ba9-dd7f-bac635d083e3@gmail.com> <10b30d8a-5c5d-a80a-e659-b5624e2848e4@gmail.com> Content-Language: en-GB From: Wol In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Archives-Salt: 7f9424f9-4756-4945-b19c-83a36048f2ee X-Archives-Hash: 0bd967002be759a0d1e4473a5242599e On 21/12/2022 06:19, Frank Steinmetzger wrote: > Am Wed, Dec 21, 2022 at 05:53:03AM +0000 schrieb Wols Lists: > >> On 21/12/2022 02:47, Dale wrote: >>> I think if I can hold out a little while, something really nice is going >>> to come along.  It seems there is a good bit of interest in having a >>> Raspberry Pi NAS that gives really good performance.  I'm talking a NAS >>> that is about the same speed as a internal drive.  Plus the ability to >>> use RAID and such.  I'd like to have a 6 bay with 6 drives setup in >>> pairs for redundancy.  I can't recall what number RAID that is. >>> Basically, if one drive fails, another copy still exists.  Of course, >>> two independent NASs would be better in my opinion.  Still, any of this >>> is progress. >> >> That's called either Raid-10 (linux), or Raid-1+0 (elsewhere). Note that 1+0 >> is often called 10, but linux-10 is slightly different. > > In layman’s term, a stripe of mirrors. Raid-1 is the mirror, Raid-0 a (JBOD) > pool. So mirror + pool = mirrorpool, hence the 1+0 → 10. Except raid-10 is not a stripe of mirrors. It's each block is saved to two different drives. (Or 3, or more, so long as you have more drives than mirrors.) Linux will happily give you a 2-copy mirror across 3 drives - 3x6TB drives will give you 9TB useful storage ... > >> I'd personally be inclined to go for raid-6. That's 4 data drives, 2 parity >> (so you could have an "any two" drive failure and still recover). >> A two-copy 10 or 1+0 is vulnerable to a two-drive failure. A three-copy is >> vulnerable to a three-drive failure. > > At first, I had only two drives in my 4-bay NAS, which were of course set up > as a mirror. After a year, when it became full, I bought the second pair of > drives and had long deliberations by then, what to choose. I went for raid-6 > (or RaidZ2 in ZFS parlance). With only four disks, it has the same net > capacity as a pair of mirrors, but at the advantage that *any* two drives > may fail, not just two particular ones. A raid of mirrors has performance > benefits over a parity raid, but who cares for a simple Gbit storage device. > > With increasing number of disks, a mirror setup is at a disadvantage with > storage efficiency – it’s always 50 % or less, if you mirror over more than > two disks. But with only four disks, that was irrelevant in my case. On the > plus-side, each mirror can have a different physical disk size, so you can > more easily mix’n’match what you got lying around, or do upgrades in smaller > increments. > > If I wanted to increase my capacity, I’d have to replace *all* drives with > bigger ones. With a mirror, only the drives in one of the mirrors need > replacing. And the rebuild process would be quicker and less painful, as > each drive will only be read once to rebuild its partner, and there is no > parity calculation involved. In a RAID, each drive is replaced one by one, > and each replacement requires a full read of all drives’ payload. If you've got a spare SATA connection or whatever, each replacement does not need a full read of all drives. "mdadm --add /dev/sdx --replace /dev/sdy". That'll stream sdy on to sdx, and only hammer the other drives if sdy complains ... > With older > drives, this is cause for some concern whether the disks may survive that. > That’s why, with increasing disk capacities, raid-5 is said to be obsolete. > Because if another drive fails during rebuild, you are officially screwed. > > Fun, innit? > They've always said that. Just make sure you don't have multiple drives from the same batch, then they're less likely statistically to fail at the same time. I'm running raid-5 over 3TB partitions ... Cheers, Wol