Date: Wed, 10 Jan 2007 12:39:19 +0100 (CET) From: Oliver Fromme <olli@lurza.secnetix.de> To: freebsd-fs@FreeBSD.ORG, freebsd@scottevil.com Subject: Re: skipping fsck with soft-updates enabled Message-ID: <200701101139.l0ABdJ9K088810@lurza.secnetix.de> In-Reply-To: <45A3C96A.6030307@scottevil.com>
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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
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