Date: Thu, 21 May 2015 12:54:21 -0600 From: Warner Losh <imp@bsdimp.com> To: Neffi <nefftd@gmail.com> Cc: hackers@freebsd.org, mav@freebsd.org, imp@freebsd.org Subject: Re: Botched NCQ on SSD - cannot disable? Message-ID: <8EDE2E6C-FED8-498B-9211-E3534A28D2FC@bsdimp.com> In-Reply-To: <CA%2BK1YHFrxHt5rVU%2BLsH9UN37dr_7or1C7rEB0eHfJisU7sPE0Q@mail.gmail.com> References: <CA%2BK1YHFrxHt5rVU%2BLsH9UN37dr_7or1C7rEB0eHfJisU7sPE0Q@mail.gmail.com>
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--Apple-Mail=_F796935C-00AE-4B10-81D6-6CC27AFD50C4 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 > On May 21, 2015, at 12:42 PM, Neffi <nefftd@gmail.com> wrote: >=20 > I was discussing this issue in freenode/#freebsd and I was recommended = to shoot an email to you fellows about it. >=20 > I've got an Samsung 840 EVO SSD (model MZ-7TE250BW), which uses = Samsung's own controller from what I can gather. I had issues of mass = data corruption when used under Linux, and several programs crashing = unexpectedly when used under FreeBSD. I've gone through 2 drives under = warranty with the same issue before customer service suggested to = disable drive queuing. >=20 > After some research it seems as though this drive (and several other = common SSDs) report that they support NCQ, but in fact are botched and = will have all sorts of problems with NCQ enabled ranging from poor = performance, to I/O stalls to data corruption. >=20 > Sure enough the logs on Linux spit out something along the lines of: >=20 > > ata1: exception Emask 0x0 SAct 0xf SErr 0x0 action 0x10 frozen > > ata1.00: failed command: READ FPDMA QUEUED >=20 > This happens several times when used on Linux, in the few hours = leading up to total filesystem corruption. >=20 > The recommendation in the Linux world is to disable NCQ on these = drives, for which there is an easy boot-time tunable for it. This fixes = the issue. No more data corruption. >=20 > There doesn't seem to be a tunable for this anywhere on FreeBSD. = camcontrol(8) mentions setting the tags used, but only between some = hardcoded limits, with a default of 2 -- not sufficient to disable NCQ = on the drive. It looks like presently the only option is to manually = patch the quirks for this drive in the kernel and recompile before I can = even install the system to the drive. One option is to use drives that don=E2=80=99t suck so bad. If you are using the AHCI controller, it has quirks for some cards that = don=E2=80=99t properly fill in the NCQ tags, but so far that=E2=80=99s a = tiny list of mostly older gear. What=E2=80=99s the host controller you = are using. Also, just because the command that hung on the drive is an NCQ command, = that doesn=E2=80=99t mean disabling NCQ commands will keep you safe. = That=E2=80=99s just the first one that=E2=80=99s issued after the = firmware wedges (or could be: that=E2=80=99s a very common scenario for = this kind of failure mode). There=E2=80=99s a quirk for the 840 EVO, but that=E2=80=99s just to = force 4k sector size. While I haven=E2=80=99t used this generation of Samsung SSDs, I=E2=80=99d = be highly surprised if this issue was really a problem in the drive = instead of some cabling issue, or other environmental issue leading the = the wedge. It=E2=80=99s true there=E2=80=99s no way to totally disable NCQ, but if = the drive is hanging with NCQ depth of 2, I=E2=80=99d be highly = surprised if it is actually NCQ causing this... Warner --Apple-Mail=_F796935C-00AE-4B10-81D6-6CC27AFD50C4 Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc Content-Description: Message signed with OpenPGP using GPGMail -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQIcBAEBCgAGBQJVXindAAoJEGwc0Sh9sBEA3HoP/3NlsC66V2bPHoi+4GaxMi47 U+fsZ74aHCWi9MBShldNCYrM3umKDj126sMNSoAZaR1/Bd5y3vF55b+wHnd+Oc2P 7+mck+3PuexqtCq9lxhqPWpM5fIZ+3t/QfQus4qHbgBjajFIX+F21vqulC0BuE/m 5vw/QBKZ3hqaHZH7mHaY83vlNwzxpY0z5UHW8B2JFTJuVU7ixu2D9b6WcFM0Dd8a 92v4MeA47Hr6H3Kv9QzfprKs7MYV8Q67AM5qvZDitHIkFzwg8dFlSVe1KZCbyQox 7ia8JfnVhj8hPJlycC9Cc2xH78VJDML6yK9HruNuwy6TBobz6PgnYk7e1T5Kj62Y yk5IH2dQxdevMGZLNrl0SpuRzszJm6ukZOgmsrENC81wJ/EpiVuVYaBlWV7jLaxU NTtL2n7/MSVecHKi7MqgoHDg/JjpUmUnCiRitY77LiQSc/oA2cnVJREQtT1mMSWM NweaQsiJwNdjs2k1XUArop2mj+2PJSg8Zqzm5djq35F9iuRnXIX9WcgUvlvVWgLr BspdwtX1aaNDt9HRyrGFjBxrd19n2K4GsswCFNRzTy/18HQHhOuVRgUT6ai+8neK kYGgU1gvKQMe30/QMbBbpruJfMDyVgFayq862L74zjeqr956PpAar/nE61JNuId9 pwm9TfQIcUsV6yk7NPXB =BdTp -----END PGP SIGNATURE----- --Apple-Mail=_F796935C-00AE-4B10-81D6-6CC27AFD50C4--
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