From owner-freebsd-stable@freebsd.org Tue Apr 30 14:12:58 2019 Return-Path: Delivered-To: freebsd-stable@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id C54DE1592BBB for ; Tue, 30 Apr 2019 14:12:58 +0000 (UTC) (envelope-from michelle@sorbs.net) Received: from hades.sorbs.net (hades.sorbs.net [72.12.213.40]) by mx1.freebsd.org (Postfix) with ESMTP id 3C0FD73096; Tue, 30 Apr 2019 14:12:58 +0000 (UTC) (envelope-from michelle@sorbs.net) MIME-version: 1.0 Content-type: text/plain; charset=utf-8 Received: from [10.10.0.230] (gate.mhix.org [203.206.128.220]) by hades.sorbs.net (Oracle Communications Messaging Server 7.0.5.29.0 64bit (built Jul 9 2013)) with ESMTPSA id <0PQS002XD2SQY400@hades.sorbs.net>; Tue, 30 Apr 2019 07:26:53 -0700 (PDT) Subject: Re: ZFS... From: Michelle Sullivan X-Mailer: iPad Mail (16A404) In-reply-to: Date: Wed, 01 May 2019 00:12:54 +1000 Cc: Karl Denninger , FreeBSD Content-transfer-encoding: quoted-printable Message-id: <6E471004-C8BC-4E9C-83B1-A9BECC0A54C4@sorbs.net> References: <30506b3d-64fb-b327-94ae-d9da522f3a48@sorbs.net> <56833732-2945-4BD3-95A6-7AF55AB87674@sorbs.net> <3d0f6436-f3d7-6fee-ed81-a24d44223f2f@netfence.it> <17B373DA-4AFC-4D25-B776-0D0DED98B320@sorbs.net> <70fac2fe3f23f85dd442d93ffea368e1@ultra-secure.de> <70C87D93-D1F9-458E-9723-19F9777E6F12@sorbs.net> <5ED8BADE-7B2C-4B73-93BC-70739911C5E3@sorbs.net> <2e4941bf-999a-7f16-f4fe-1a520f2187c0@sorbs.net> To: Alan Somers X-Rspamd-Queue-Id: 3C0FD73096 X-Spamd-Bar: --- Authentication-Results: mx1.freebsd.org; spf=pass (mx1.freebsd.org: domain of michelle@sorbs.net designates 72.12.213.40 as permitted sender) smtp.mailfrom=michelle@sorbs.net X-Spamd-Result: default: False [-3.05 / 15.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; NEURAL_HAM_MEDIUM(-1.00)[-0.999,0]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_THREE(0.00)[3]; R_SPF_ALLOW(-0.20)[+a:hades.sorbs.net]; NEURAL_HAM_LONG(-1.00)[-1.000,0]; MIME_GOOD(-0.10)[text/plain]; DMARC_NA(0.00)[sorbs.net]; TO_MATCH_ENVRCPT_SOME(0.00)[]; TO_DN_ALL(0.00)[]; MX_GOOD(-0.01)[cached: battlestar.sorbs.net]; NEURAL_HAM_SHORT(-0.55)[-0.545,0]; RCVD_IN_DNSWL_NONE(0.00)[40.213.12.72.list.dnswl.org : 127.0.10.0]; SUBJ_ALL_CAPS(0.45)[6]; IP_SCORE(-0.75)[ip: (-1.98), ipnet: 72.12.192.0/19(-0.96), asn: 11114(-0.74), country: US(-0.06)]; RCVD_NO_TLS_LAST(0.10)[]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; ASN(0.00)[asn:11114, ipnet:72.12.192.0/19, country:US]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2] X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 30 Apr 2019 14:12:58 -0000 Michelle Sullivan http://www.mhix.org/ Sent from my iPad > On 01 May 2019, at 00:01, Alan Somers wrote: >=20 >>>=20 >>> Unfortunately however there is also cache memory on most modern hard >>> drives, most of the time (unless you explicitly shut it off) it's on for= >>> write caching, and it'll nail you too. Oh, and it's never, in my >>> experience, ECC. >=20 > Fortunately, ZFS never sends non-checksummed data to the hard drive. > So an error in the hard drive's cache ram will usually get detected by > the ZFS checksum. True, but a drive losing power mid write will ensure the checksum doesn=E2=80= =99t match the data (even if it is written before the data)... you need to e= nsure all the data and the checksum is written before drive power down.. and= in the event of unexpected hard power fail, you can=E2=80=99t guarantee thi= s. Battery backup in the controller that has a write cache and re-writes th= e last few writes on power restore on the otherhand will save you.. which is= why the other machine at my disposal hasn=E2=80=99t failed to date. Michelle=