Date: Sat, 10 Dec 2011 17:02:16 +0200 From: Arto Pekkanen <isoa@kapsi.fi> To: freebsd-questions@freebsd.org Subject: Re: 9.0 install and journaling Message-ID: <4EE37478.4000109@kapsi.fi> In-Reply-To: <4EE36250.6090503@herveybayaustralia.com.au> References: <4EE32BB6.3020105@herveybayaustralia.com.au> <20111210114053.GA69009@orange.esperance-linux.co.uk> <20111210122042.2b355bc6@gumby.homeunix.com> <4EE36250.6090503@herveybayaustralia.com.au>
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On 10.12.2011 15:44, Da Rock wrote: > So how does soft-update journaling compare to gjournal? I'm using gjournal now > and it runs a bit of a dog, but it is reliable (until another ufs filesystem > turns up at boot) and necessary in my environment. Can I dump it for this new one? > > Its used on a laptop with heavy load on the disk, the power on the battery can > run out too quick for batterymon to shut it down- plus kids that play silly > monkeys with daddy's laptop... :) > _______________________________________________ > freebsd-questions@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-questions > To unsubscribe, send any mail to "freebsd-questions-unsubscribe@freebsd.org" I am not an expert, but this is how I currently understand this: Geom-journal is a block level journaling mechanism. It means that all data written on a journaled provider will be first written to the providers journal and then later commited to the provider. Thus data is written twice to provide more redundancy. Soft-updates by itself has nothing to do with any journaling. It simply makes synchronous writes faster. When a filesystem is mounted synchronously, each write to a file first updates the metadata of the file, such a file size, and after that writes the actual data into the disk. When doing operations on thousands of small files, the overhead from synchronous writing is considerable. Bring forth soft-updates, which caches the metadata (file size etc.) updates into ram, and commits these updates into disk later when a delay and some conditions trigger; actual data is written into disk as soon as possible. Thus append/random access operations on gazillion of files are a lot faster. From this I would conclude that soft-updates journaling tries to write the metadata updates into a filesystem spesific soft-update journal (the soft-update journal being a file maybe?) sooner than they are actually committed. I also suspect that soft-updates journaling has some clever way of detecting when it is, performance wise, okay to update the journal and/or commit updates. In short: - gjournal writes both data and metadata, providing more redundancy to the actual data AND filesystem integrity while slowing down write operations (although I do not have data how much it slows down disk i/o) - journaled soft-updates writes metadata updates twice on the disk, providing redundancy to file system integrity, but does not prevent actual data loss. I do not even use FreeBSD 9.0 myself, my information is totally third party, second hand, wise-cracks and guessing. Any expert consultation would be appreciated. -- Arto Pekkanen ksym@IRCnet
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