Date: Wed, 01 May 2019 00:12:54 +1000 From: Michelle Sullivan <michelle@sorbs.net> To: Alan Somers <asomers@freebsd.org> Cc: Karl Denninger <karl@denninger.net>, FreeBSD <freebsd-stable@freebsd.org> Subject: Re: ZFS... Message-ID: <6E471004-C8BC-4E9C-83B1-A9BECC0A54C4@sorbs.net> In-Reply-To: <CAOtMX2gOwwZuGft2vPpR-LmTpMVRy6hM_dYy9cNiw%2Bg1kDYpXg@mail.gmail.com> References: <30506b3d-64fb-b327-94ae-d9da522f3a48@sorbs.net> <CAOtMX2gf3AZr1-QOX_6yYQoqE-H%2B8MjOWc=eK1tcwt5M3dCzdw@mail.gmail.com> <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> <CAGMYy3tYqvrKgk2c==WTwrH03uTN1xQifPRNxXccMsRE1spaRA@mail.gmail.com> <5ED8BADE-7B2C-4B73-93BC-70739911C5E3@sorbs.net> <d0118f7e-7cfc-8bf1-308c-823bce088039@denninger.net> <2e4941bf-999a-7f16-f4fe-1a520f2187c0@sorbs.net> <CAOtMX2gOwwZuGft2vPpR-LmTpMVRy6hM_dYy9cNiw%2Bg1kDYpXg@mail.gmail.com>
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Michelle Sullivan http://www.mhix.org/ Sent from my iPad > On 01 May 2019, at 00:01, Alan Somers <asomers@freebsd.org> 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=
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