Date: Thu, 11 Jan 2007 10:04:39 -0600 From: Eric Anderson <anderson@centtech.com> To: Brooks Davis <brooks@one-eyed-alien.net> Cc: freebsd-fs@freebsd.org Subject: Re: skipping fsck with soft-updates enabled Message-ID: <45A66017.30003@centtech.com> In-Reply-To: <20070110174337.GA7544@lor.one-eyed-alien.net> References: <45A3C96A.6030307@scottevil.com> <200701101139.l0ABdJ9K088810@lurza.secnetix.de> <ac00e00a0701100538m16395e87t2fbf69acfeeb04ed@mail.gmail.com> <45A485C6.2060405@scottevil.com> <45A5024F.10502@centtech.com> <20070110174337.GA7544@lor.one-eyed-alien.net>
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On 01/10/07 11:43, Brooks Davis wrote: > On Wed, Jan 10, 2007 at 09:12:15AM -0600, Eric Anderson wrote: >> On 01/10/07 00:20, Scott Oertel wrote: >>> Victor Loureiro Lima wrote: >>> >From rc.conf man page: >>>> --- >>>> background_fsck_delay >>>> (int) The amount of time in seconds to sleep before >>>> starting >>>> a background fsck(8). It defaults to sixty seconds to >>>> allow >>>> large applications such as the X server to start >>>> before disk >>>> I/O bandwidth is monopolized by fsck(8). >>>> --- >>>> >>>> You can set the delay as long as you want, so it wont have to start >>>> right away, in fact it can start as late as a year (if thats really >>>> what you want ;)) >>>> >>>> att, >>>> victor loureiro lima >>>> >>>> 2007/1/10, Oliver Fromme <olli@lurza.secnetix.de>: >>>>> Scott Oertel wrote: >>>>>> I am wondering what kind of problems would occur, besides lost >>>>> space, if >>>>>> after a system crash a fsck is skipped. According to the >>>>> documentation, >>>>>> with soft-updates enabled, the file system would be consistant, there >>>>>> would just be lost resources to be recovered which I am assuming >>>>> can be >>>>>> safely done at a later time to avoid long periods of downtime during >>>>>> peek hours. >>>>> I think that's exactly what the background fsck feature >>>>> does. If you enable it (which is even the default), the >>>>> fsck process doesn' start right away, so the system comes >>>>> up in multi-user mode immediately. Then a snapshot is >>>>> created on the file system, and fsck runs on the snap- >>>>> shot, freeing the lost space in the file system. >>>>> >>>>> Of course, it only works reliably with soft-updates enabled, >>>>> _and_ there must not be any unexpected inconsistencies. >>>>> However, with some common setups (e.g. cheap disks lying >>>>> about completed write operation) it is difficult to >>>>> guarantee the consistency. Soft-updates is rather fragile >>>>> when the hardware doesn't work exactly as it's supposed to. >>>>> I've witnessed breakage in the past, and for that reason >>>>> I always disable the background fsck feature. And it's the >>>>> reason I'm looking forward to gjournal to become stable, >>>>> because it seems to be less fragile in the presence of >>>>> imperfect hardware. >>>>> >>>>> Best regards >>>>> Oliver >>>>> >>>>> -- >>>>> Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing >>>>> Dienstleistungen mit Schwerpunkt FreeBSD: http://www.secnetix.de/bsd >>>>> Any opinions expressed in this message may be personal to the author >>>>> and may not necessarily reflect the opinions of secnetix in any way. >>>>> >>>>> "C++ is to C as Lung Cancer is to Lung." >>>>> -- Thomas Funke >>>>> _______________________________________________ >>> The problem with background fsck is that on my machines, it doesn't work >>> well. These machines have 8x750gb SATA drives and they are under extreme >>> stress all the time. When you run fsck in the background each drive >>> takes 10+ minutes to create the snapshot file, during which time the >>> machine is completely unresponsive, and unstable. >> What version of FreeBSD are you running? You might try gjournal, which >> I've had great luck with, and Pawel (pjd@) is incredibly responsive to >> bug reports, etc. >> >>> That is why I am wondering, if it is ok to skip the background fsck's, >>> foreground fsck's and reschedule them for a later time, during non peak >>> hours. >> I think most people would be nervous to tell you 'sure, skip it until >> later', but I can tell you from experience that I myself have delayed >> fscking for weeks on end, to do exactly what you want. > > I've been thinking it would be useful to have a new background_fsck_delay > value of CRON and have a cron job that can accomplish the background > fsck during off hours if needed. > > -- Brooks I think an even better solution is to have a "NONE" option, that never does it. Then, you can just cron it whenever if you wish, or never if you wish. NONE is also more consistent with other rc-like options (I think). Eric -- ------------------------------------------------------------------------ Eric Anderson Sr. Systems Administrator Centaur Technology An undefined problem has an infinite number of solutions. ------------------------------------------------------------------------
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