Date: Tue, 30 Apr 2019 08:11:29 -0500 From: Karl Denninger <karl@denninger.net> To: freebsd-stable@freebsd.org Subject: Re: ZFS... Message-ID: <d0118f7e-7cfc-8bf1-308c-823bce088039@denninger.net> In-Reply-To: <5ED8BADE-7B2C-4B73-93BC-70739911C5E3@sorbs.net> 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>
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This is a cryptographically signed message in MIME format. --------------ms050501030002040403040807 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 4/30/2019 05:14, Michelle Sullivan wrote: >> On 30 Apr 2019, at 19:50, Xin LI <delphij@gmail.com> wrote: >>> On Tue, Apr 30, 2019 at 5:08 PM Michelle Sullivan <michelle@sorbs.net= > wrote: >>> but in my recent experience 2 issues colliding at the same time resul= ts in disaster >> Do we know exactly what kind of corruption happen to your pool? If yo= u see it twice in a row, it might suggest a software bug that should be i= nvestigated. >> >> All I know is it=E2=80=99s a checksum error on a meta slab (122) and f= rom what I can gather it=E2=80=99s the spacemap that is corrupt... but I = am no expert. I don=E2=80=99t believe it=E2=80=99s a software fault as s= uch, because this was cause by a hard outage (damaged UPSes) whilst resil= vering a single (but completely failed) drive. ...and after the first ou= tage a second occurred (same as the first but more damaging to the power = hardware)... the host itself was not damaged nor were the drives or contr= oller. =2E.... >> Note that ZFS stores multiple copies of its essential metadata, and in= my experience with my old, consumer grade crappy hardware (non-ECC RAM, = with several faulty, single hard drive pool: bad enough to crash almost m= onthly and damages my data from time to time), > This was a top end consumer grade mb with non ecc ram that had been run= ning for 8+ years without fault (except for hard drive platter failures.)= =2E Uptime would have been years if it wasn=E2=80=99t for patching. Yuck. I'm sorry, but that may well be what nailed you. ECC is not just about the random cosmic ray.=C2=A0 It also saves your bac= on when there are power glitches. 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.=C2=A0 Oh, and it's never, in my experience, ECC. In addition, however, and this is something I learned a LONG time ago (think Z-80 processors!) is that as in so many very important things "two is one and one is none." In other words without a backup you WILL lose data eventually, and it WILL be important. Raidz2 is very nice, but as the name implies it you have two redundancies.=C2=A0 If you take three errors, or if, God forbid, you *wri= te* a block that has a bad checksum in it because it got scrambled while in RAM, you're dead if that happens in the wrong place. > Yeah.. unlike UFS that has to get really really hosed to restore from b= ackup with nothing recoverable it seems ZFS can get hosed where issues oc= cur in just the wrong bit... but mostly it is recoverable (and my experie= nce has been some nasty shit that always ended up being recoverable.) > > Michelle=20 Oh that is definitely NOT true.... again, from hard experience, including (but not limited to) on FreeBSD. My experience is that ZFS is materially more-resilient but there is no such thing as "can never be corrupted by any set of events."=C2=A0 Backup= strategies for moderately large (e.g. many Terabytes) to very large (e.g. Petabytes and beyond) get quite complex but they're also very necessary. --=20 Karl Denninger karl@denninger.net <mailto:karl@denninger.net> /The Market Ticker/ /[S/MIME encrypted email preferred]/ --------------ms050501030002040403040807 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgMFADCABgkqhkiG9w0BBwEAAKCC DdgwggagMIIEiKADAgECAhMA5EiKghDOXrvfxYxjITXYDdhIMA0GCSqGSIb3DQEBCwUAMIGL MQswCQYDVQQGEwJVUzEQMA4GA1UECAwHRmxvcmlkYTESMBAGA1UEBwwJTmljZXZpbGxlMRkw FwYDVQQKDBBDdWRhIFN5c3RlbXMgTExDMRgwFgYDVQQLDA9DdWRhIFN5c3RlbXMgQ0ExITAf 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