Date: Wed, 10 Jan 2007 09:12:15 -0600 From: Eric Anderson <anderson@centtech.com> To: Scott Oertel <freebsd@scottevil.com> Cc: freebsd-fs@freebsd.org Subject: Re: skipping fsck with soft-updates enabled Message-ID: <45A5024F.10502@centtech.com> In-Reply-To: <45A485C6.2060405@scottevil.com> References: <45A3C96A.6030307@scottevil.com> <200701101139.l0ABdJ9K088810@lurza.secnetix.de> <ac00e00a0701100538m16395e87t2fbf69acfeeb04ed@mail.gmail.com> <45A485C6.2060405@scottevil.com>
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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. Eric -- ------------------------------------------------------------------------ Eric Anderson Sr. Systems Administrator Centaur Technology An undefined problem has an infinite number of solutions. ------------------------------------------------------------------------
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