Date: Sun, 12 Dec 1999 12:24:14 +0100 From: Mattias Pantzare <pantzer@ludd.luth.se> To: Jay Nelson <noslenj@swbell.net> Cc: chat@FreeBSD.ORG Subject: Re: Log file systems? (Was: Re: dual 400 -> dual 600 worth it?) Message-ID: <199912121124.MAA25648@zed.ludd.luth.se> In-Reply-To: Message from Jay Nelson <noslenj@swbell.net> of "Sat, 11 Dec 1999 19:25:09 CST." <Pine.BSF.4.05.9912111914020.2035-100000@acp.swbell.net>
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> >How similar is that to the log partition in SGI's XFS? There was no > >restriction as to what spindle the log filesystem was placed. Quite to > >the contrary, it was indicated using a separate drive on a separate > >SCSI bus would help performance. > > XFS sounds a lot like AIX's JFS. Which raises the question: What is > the connection between BSD's lfs, soft updates, SGI's XFS and AIX's > jfs? Don't they all do essentially the same thing except for where the > log is written? No. lfs is a logging filesystem. You only have a log that contains everything, including all your files. The downside to this is that you have to have a garbage collector that cleans deleted data from the log. The good thing is that you never have to seek for writes. All writes are to the end of the log. http://www.cs.berkeley.edu/projects/sprite/papers/ has some papers on lfs. A journaling filesystem is like a normal filesystem but you have a transaction log that turns synchronous writes into a synchronous write to the log and a asynchronous write to the normal filesystem. This avoids seeks when latency is important. Soft updates do not have a log att all. Take a look at http://www.ece.cmu.edu/~ganger/papers/CSE-TR-254-95/. Lfs will not roll in the normal sense, it will simply discard the half done write at the end of the log if there is one. Soft updates can't do rolling as there is no log. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-chat" in the body of the message
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