From owner-freebsd-hackers  Fri May 25 13:29:14 2001
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From: Terry Lambert <tlambert@primenet.com>
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Subject: Re: technical comparison
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Date: Fri, 25 May 2001 20:37:13 +0000 (GMT)
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] > ] > 1. I don't think I've ever seen a Linux distro which has write
] > ] >    caching enabled by default. Hell, DMA33 isn't even enabled
] > ] >    by default ;)
] > ] 
] > ] You are talking about controlling the IDE drive cache.
] > ] 
] > ] The issue here is write cache in the filesystem code.
] > 
] > No.  The issue here is the write cache on the drive.
] > FreeBSD with soft updates will operate within 4% of the top memory
] > bandwidth; see the Ganger/Patt paper on the technology.
] 
] I have a file, CSE-TR-254-95.ps, that I think is probably the paper
] you are talking about. The title is "Soft Updates: A Solution to the
] Metadata Update Problem in File Systems". The link on Ganger's page was
] dead, but I'm sure this is the one you mean.
] 
] Nowhere do they support the idea that soft udpates can approach a
] system's memory bandwidth.

I said "top memory bandwidth", not "a system's memory bandwidth";
please be more careful.

Quoting from section 6, "Conclusions and Future Work":

	We have described a new mechanism, soft updates, that
	can be used to achieve memory-based file system
	                       ************************
	performance while providing stronger integrity and
	***********

	security guarantees (e.g. allocation initialization)
	and higher availability (via shorter recovery times)
	than most UNIX file systems.  This translates into a
	performance improvement of more than a factor fo 2
	in many cases (up to a maximum observed difference
	of a factor of 15).


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.

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