From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from twosheds.infradead.org ([2001:8b0:10b:1:21d:7dff:fe04:dbe2]) by bombadil.infradead.org with esmtps (Exim 4.87 #1 (Red Hat Linux)) id 1d7cze-0001gs-KR for linux-mtd@lists.infradead.org; Mon, 08 May 2017 07:22:06 +0000 Message-ID: <1494228094.6528.14.camel@infradead.org> Subject: Re: Race to power off harming SATA SSDs From: David Woodhouse To: Pavel Machek , Tejun Heo Cc: Henrique de Moraes Holschuh , linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org, Hans de Goede , boris.brezillon@free-electrons.com, linux-mtd@lists.infradead.org In-Reply-To: <20170507204007.GA25628@atrey.karlin.mff.cuni.cz> References: <20170410232118.GA4816@khazad-dum.debian.net> <20170410235206.GA28603@wtj.duckdns.org> <20170507204007.GA25628@atrey.karlin.mff.cuni.cz> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-fVZRLoxOMkwA6Oz2UYSn" Date: Mon, 08 May 2017 08:21:34 +0100 Mime-Version: 1.0 List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , --=-fVZRLoxOMkwA6Oz2UYSn Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sun, 2017-05-07 at 22:40 +0200, Pavel Machek wrote: > > > NOTE: unclean SSD power-offs are dangerous and may brick the device i= n > > > the worst case, or otherwise harm it (reduce longevity, damage flash > > > blocks).=C2=A0=C2=A0It is also not impossible to get data corruption. > > > I get that the incrementing counters might not be pretty but I'm a bit > > skeptical about this being an actual issue.=C2=A0=C2=A0Because if that = were > > true, the device would be bricking itself from any sort of power > > losses be that an actual power loss, battery rundown or hard power off > > after crash. > > And that's exactly what users see. If you do enough power fails on a > SSD, you usually brick it, some die sooner than others. There was some > test results published, some are here > http://lkcl.net/reports/ssd_analysis.html, I believe I seen some > others too. >=20 > It is very hard for a NAND to work reliably in face of power > failures. In fact, not even Linux MTD + UBIFS works well in that > regards. See > http://www.linux-mtd.infradead.org/faq/ubi.html. (Unfortunately, its > down now?!). If we can't get it right, do you believe SSD manufactures > do? >=20 > [Issue is, if you powerdown during erase, you get "weakly erased" > page, which will contain expected 0xff's, but you'll get bitflips > there quickly. Similar issue exists for writes. It is solveable in > software, just hard and slow... and we don't do it.] It's not that hard. We certainly do it in JFFS2. I was fairly sure that it was also part of the design considerations for UBI =E2=80=94 it really o= ught to be right there too. I'm less sure about UBIFS but I would have expected it to be OK. SSDs however are often crap; power fail those at your peril. And of course there's nothing you can do when they do fail, whereas we accept patches for things which are implemented in Linux. --=-fVZRLoxOMkwA6Oz2UYSn Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCDzUw ggSvMIIDl6ADAgECAhEA4CPLFRKDU4mtYW56VGdrITANBgkqhkiG9w0BAQsFADBvMQswCQYDVQQG EwJTRTEUMBIGA1UEChMLQWRkVHJ1c3QgQUIxJjAkBgNVBAsTHUFkZFRydXN0IEV4dGVybmFsIFRU UCBOZXR3b3JrMSIwIAYDVQQDExlBZGRUcnVzdCBFeHRlcm5hbCBDQSBSb290MB4XDTE0MTIyMjAw MDAwMFoXDTIwMDUzMDEwNDgzOFowgZsxCzAJBgNVBAYTAkdCMRswGQYDVQQIExJHcmVhdGVyIE1h bmNoZXN0ZXIxEDAOBgNVBAcTB1NhbGZvcmQxGjAYBgNVBAoTEUNPTU9ETyBDQSBMaW1pdGVkMUEw PwYDVQQDEzhDT01PRE8gU0hBLTI1NiBDbGllbnQgQXV0aGVudGljYXRpb24gYW5kIFNlY3VyZSBF bWFpbCBDQTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAImxDdp6UxlOcFIdvFamBia3 uEngludRq/HwWhNJFaO0jBtgvHpRQqd5jKQi3xdhTpHVdiMKFNNKAn+2HQmAbqUEPdm6uxb+oYep 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