Date: Thu, 14 Nov 2013 21:04:23 +0000 From: "Teske, Devin" <Devin.Teske@fisglobal.com> To: Marcus Reid <marcus@blazingdot.com> Cc: freebsd-fs <freebsd-fs@freebsd.org>, Devin Teske <dteske@freebsd.org>, "Teske, Devin" <Devin.Teske@fisglobal.com>, FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: Defaults in 10.0 ZFS through bsdinstall Message-ID: <B79068CE-A0CB-49B5-ABD1-5135A5F547BD@fisglobal.com> In-Reply-To: <20131114203424.GA22267@blazingdot.com> References: <20131114173423.GA21761@blazingdot.com> <59A9B68B-4134-4217-83F3-B99759174EFE@fisglobal.com> <5285148E.6020903@allanjude.com> <3D3332FA-0ABF-4573-8E65-4E7FBB37100B@fisglobal.com> <20131114203424.GA22267@blazingdot.com>
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On Nov 14, 2013, at 12:34 PM, Marcus Reid wrote: > On Thu, Nov 14, 2013 at 06:35:43PM +0000, Teske, Devin wrote: >> On Nov 14, 2013, at 10:21 AM, Allan Jude wrote: >>> On 2013-11-14 9:34, Reid, Marcus wrote: >>>=20 >>> Hi, >>>=20 >>> I noticed a couple of things with the ZFS defaults that result from >>> using the new installer in 10.0-BETA3. >>>=20 >>> One, atime is turned off everywhere by default. There was a thread >>> on this list on June 8 with a subject of 'Changing the default for >>> ZFS atime to off?', and from what I can tell the idea of turning off >>> atime by default was not a popular one. >>>=20 >>> Two, and probably less controversial, is that fletcher4 is specified >>> exlicitly on the root pool, even though it is default (wouldn't you >>> just want to go with the default, in case it changes?) >>>=20 >>> Marcus >>=20 >> I have never heard a good argument for having atime on. >=20 > Can you address some of the issues that people brought up in the thread > I mentioned earlier? I'll summarize some: >=20 > - breaks some software (MTAs were mentioned), and the admin should > know when to turn atime on in those cases. >=20 > - "any mail program using mbox mail folders uses them to correctly > report which mailboxes have not been read yet" >=20 I'm looking at HEAD and I don't see "atime=3Doff" for the /var dataset. Knowing that most folks (accepting the defaults) will store their mail in /var/mail ... does the concern over atime=3Doff still exist? However, I did notice that before we go creating the /var dataset, we do set "atime=3Doff" for the boot pool/dataset. Is inheritance at-play here? and /var is turning up with atime=3Doff even though it's not specified? In that case, I certainly agree we should remove atime=3Doff from the last place it is used -- the boot pool (nowhere else). > - "Of course it can't be turned off by default. It is specified by > POSIX." >=20 > - "If the overhead were a real problem then file systems would use a > special atime cache" >=20 >> The performance penalty on ZFS is quite large >=20 > This is subjective, and if it were that bad it seems like other > ZFS-based systems would have turned it off as well, or done something > like caching/logging or relatime it to mitigate the performance hit. >=20 I do recall discussions about bringing over relatime and making it the default. Allan was the one that brought up the performance hit... Similarly where I $work, we turn it off where need performance (large storage arrays and such). I gather it's only a matter of time until relatime is default. >> and it also makes your snapshots grow constant. >=20 > This does not seem to be the case. For example, if I snapshot > zroot/usr/src and then tar it up, I generate a bunch of writes and the > snapshot grows to 70.5MB. However, when I tar it up a second time, > there are writes but the snapshot remains 70.5MB. It seems to use the > same blocks for subsequent atime updates. >=20 > If you made another snapshot, you would see more space used for that > one, of course. >=20 I'll defer to Allan to expand (was his recollection on snapshots) >> If you have a use for it, you can turn it on I guess. This would be >> solved by having the dataset editor we're planning for 10.1 >>=20 >> Seems easy enough to turn on once installed. And like Allan says, the >> editor for 10.1 would allow changing of the default. >=20 > The same case could be made for turning it off, make that an option in > the installer instead. >=20 Fair enough. Good idea. > Some people don't seem to use atime on a regular basis, but I use it a > lot when troubleshooting things, and I think others do to when they get > to the point where they realize how useful it is. >=20 >> I'll add that if scripting it, you can (in current state for 10.0) >> change the dataset options at-will. >>=20 >> The fletcher4 thing is a leftover, from older versions of ZFS where >> the default was fletcher2, I suppose we can remove it >=20 > While I'm picking nits: >=20 > There are some other locally set things that are default (exec set to on > on zroot/var/tmp is one), that might just inherit that from zroot/var. >=20 Need a +1 from Allan on that. > Also, zroot doesn't appear to be mounted on /zroot, as it is on other > ZFS-based systems. This has the side-effect of newly created > datasets not having a mountpoint by default, instead of /zroot/dataset. > I don't know of the reason behind this change either. >=20 Hmm, wonder if that's been fixed in HEAD already. > I'm going to cross-post this to -current, this is a topic that I think > warrants a wider audience. >=20 Cool. Thanks. --=20 Devin >> -----BEGIN PGP SIGNATURE----- >> Comment: GPGTools - https://urldefense.proofpoint.com/v1/url?u=3Dhttps:/= /gpgtools.org/&k=3D%2FbkpAUdJWZuiTILCq%2FFnQg%3D%3D%0A&r=3DLTzUWWrRnz2iN3Pt= HDubWRSAh9itVJ%2BMUcNBCQ4tyeo%3D%0A&m=3DwXwxswJCpc3K%2Bud90aYI%2B82v%2Fyfs1= mrTBzzeCe5XIXw%3D%0A&s=3Da9e0697e43ce4744f130997648d0104319221bba6924c28a94= 93ffa1cf6c3719 >>=20 >> iQEcBAEBCgAGBQJShRf/AAoJEKrMn5R9npq5TYwH/j8RMceM4STpCAoMTAz8zkKn >> gpftMrdf37TnAPHxsXJaiZejlp+D85/a9lglYbB7e4WdgoDX9ZXA0QLtCEmEtN4y >> jz7KNa5oABq1GjDtwm2xQISDIe8yYI+znLSaHA9W18kCUZzi8AOj70C+O5gyY28c >> c3N3j6Y4EZP2wtQnWSgxvCwIX5p86Jvr3QvhrRuuMnKMCTAhzwIx24qcnA4EcTzn >> p9w25CKLtOzF23n3McodaUmibbBCHOYyraLQJ+eJGDXcsPBipls3oiWyiYuqpcQr >> 18QpLN1lS35RnULcb5pxnP9Oy9rAwxHKves9Mfu0UoWw3qTjSAf8gsGyu6QaMgc=3D >> =3DGjYk >> -----END PGP SIGNATURE----- >>=20 >> _____________ >> The information contained in this message is proprietary and/or confiden= tial. 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