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: >>> >>> Hi, >>> >>> I noticed a couple of things with the ZFS defaults that result from >>> using the new installer in 10.0-BETA3. >>> >>> 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. >>> >>> 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?) >>> >>> Marcus >> >> I have never heard a good argument for having atime on. > > Can you address some of the issues that people brought up in the thread > I mentioned earlier? I'll summarize some: > > - breaks some software (MTAs were mentioned), and the admin should > know when to turn atime on in those cases. > > - "any mail program using mbox mail folders uses them to correctly > report which mailboxes have not been read yet" >
I'm looking at HEAD and I don't see "atime=off" for the /var dataset. Knowing that most folks (accepting the defaults) will store their mail in /var/mail ... does the concern over atime=off still exist? However, I did notice that before we go creating the /var dataset, we do set "atime=off" for the boot pool/dataset. Is inheritance at-play here? and /var is turning up with atime=off even though it's not specified? In that case, I certainly agree we should remove atime=off 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." > > - "If the overhead were a real problem then file systems would use a > special atime cache" > >> The performance penalty on ZFS is quite large > > 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. > 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. > > 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. > > If you made another snapshot, you would see more space used for that > one, of course. > 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 >> >> Seems easy enough to turn on once installed. And like Allan says, the >> editor for 10.1 would allow changing of the default. > > The same case could be made for turning it off, make that an option in > the installer instead. > 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. > >> I'll add that if scripting it, you can (in current state for 10.0) >> change the dataset options at-will. >> >> The fletcher4 thing is a leftover, from older versions of ZFS where >> the default was fletcher2, I suppose we can remove it > > While I'm picking nits: > > 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. > 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. > 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. > Cool. Thanks. -- Devin >> -----BEGIN PGP SIGNATURE----- >> Comment: GPGTools - >> https://urldefense.proofpoint.com/v1/url?u=https://gpgtools.org/&k=%2FbkpAUdJWZuiTILCq%2FFnQg%3D%3D%0A&r=LTzUWWrRnz2iN3PtHDubWRSAh9itVJ%2BMUcNBCQ4tyeo%3D%0A&m=wXwxswJCpc3K%2Bud90aYI%2B82v%2Fyfs1mrTBzzeCe5XIXw%3D%0A&s=a9e0697e43ce4744f130997648d0104319221bba6924c28a9493ffa1cf6c3719 >> >> iQEcBAEBCgAGBQJShRf/AAoJEKrMn5R9npq5TYwH/j8RMceM4STpCAoMTAz8zkKn >> gpftMrdf37TnAPHxsXJaiZejlp+D85/a9lglYbB7e4WdgoDX9ZXA0QLtCEmEtN4y >> jz7KNa5oABq1GjDtwm2xQISDIe8yYI+znLSaHA9W18kCUZzi8AOj70C+O5gyY28c >> c3N3j6Y4EZP2wtQnWSgxvCwIX5p86Jvr3QvhrRuuMnKMCTAhzwIx24qcnA4EcTzn >> p9w25CKLtOzF23n3McodaUmibbBCHOYyraLQJ+eJGDXcsPBipls3oiWyiYuqpcQr >> 18QpLN1lS35RnULcb5pxnP9Oy9rAwxHKves9Mfu0UoWw3qTjSAf8gsGyu6QaMgc= >> =GjYk >> -----END PGP SIGNATURE----- >> >> _____________ >> The information contained in this message is proprietary and/or >> confidential. 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