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From: Terry Lambert <terry@lambert.org>
Newsgroups: comp.unix.bsd.freebsd.misc,comp.os.linux.development.system
Subject: Re: The better (more suitable)Unix?? FreeBSD or Linux
Date: 16 Feb 1996 00:38:13 GMT
Organization: Utah Valley State College, Orem, Utah
Lines: 84
Message-ID: <4g0jll$8l9@park.uvsc.edu>
References: <4er9hp$5ng@orb.direct.ca> <311C5EB4.2F1CF0FB@freebsd.org> <4fjodg$o8k@venger.snds.com> <4fo1tu$n31@news.jf.intel.com> <4frdur$hq@galaxy.ucr.edu>
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Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:14366 comp.os.linux.development.system:18024
grif@corsa.ucr.edu (Michael Griffith) wrote:
] In article <4fo1tu$n31@news.jf.intel.com>,
] Mike Haertel <haertel@ichips.intel.com> wrote:
] |Then they claim that async metadata update is superior,
] |because it doesn't have this problem.
] |
] |FALSE!
]
] You are quite correct. If I was misleading in this regard, I
] apologize. The real intent of the discussion was to show that
] async was no worse than sync metadata. However, if you add
] ordered writes, you eliminate the problem.
Sync metadata is an implementation of ordered writes. It's
about as trivial an implementation as you can possibly devise,
but it *is* one.
If you keep confusing the issues of container object content
integrity and general referential integrity, I will have to
keep correcting you.
] The performance implications are quite substantial AND sync
] metadata doesn't really gain you anything in terms of reliability
] (it may actually hurt a bit, because you are more likely to have
] unordered writes.) Given this, why bother with sync metadata?
Wrong again. Ugh. Please read:
http://www.pdos.lcs.mit.edu/~ganger/papers/osdi94.ps.Z
Metadata Update Performance in File Systems ,
by Gregory R. Ganger and Yale N. Patt.
Appears in the Proceedings of the USENIX Symposium on
Operating Systems Design and Implementation (OSDI) ,
Nov. 1994, pp. 49-60.
Also read:
http://www.pdos.lcs.mit.edu/~ganger/papers/CSE-TR-254-95/CSE_TR_254_95.ps.Z
Soft Updates: A Solution to the Metadata Update Problem
in File Systems ,
by Gregory R. Ganger and Yale N. Patt.
Published as report number CSE-TR-254-95 by the University
of Michigan, Ann Arbor, in August 1995.
] Having inconsistent filesystem structures really isn't the issue. A
] hard failure where you know you have to restore from backups because
] fsck can't figure things out is a lot better than silently corrupting
] data.
Any time you boot a system and the clean bit wasn't set during
the shutdown process, you may have "silently correpted data".
Write your applications so that they recover from container
object failures and get over it already.
] The study may be worthwhile, but I am holding out for ordered
] writes.
Ordered writes don't do anything in terms of file system consistency
that synchronous writes already do. Ordered writes just have a
higher concurrency than synchronous writes. There is no other
effective difference.
] A comparison between properly ordered writes and the current
] situation would me much more interesting. Anybody have good
] ideas for the setup of the experiments?
You can only prove failure experimentally; you can not prove
success.
Just because it didn't fail on you when you were using it doesn't
mean that it will never fail.
Terry Lambert
terry@cs.weber.edu
---
Any opinions in this posting are my own and not those of my present
or previous employers.