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From: dml@rabbit1.UUCP
Newsgroups: net.decus,net.unix,net.usenix
Subject: Re: Re: Favorite operating systems query
Message-ID: <176@rabbit1.UUCP>
Date: Tue, 24-Jun-86 12:32:38 EDT
Article-I.D.: rabbit1.176
Posted: Tue Jun 24 12:32:38 1986
Date-Received: Sat, 28-Jun-86 03:36:23 EDT
References: <243@nyit.UUCP>
Organization: Rabbit Software Corp., Malvern PA
Lines: 40
Xref: watmath net.decus:374 net.unix:8418 net.usenix:628

> 
>> >6) File system.  Why, oh, why, must the Unix file system be so fragile?  VMS
>> >   never loses your files.
>> I can count on the fingers of one foot the number of times I have lost a
>> file due to "file system fragility" in the last 5 years on a Unix
>> system.  This "myth" is just that, and it's time to lay it to rest.
>>
>> ...
>>
>> =Spencer   ({ihnp4,decvax}!utah-cs!thomas, thomas@utah-cs.ARPA)
> 
> Well, almost a myth.  UNIX filesystem implementations (even the touted
> one in 4.2bsd) trade off filesystem integrity for speed in places
> where other operating systems give you the guarantee that your data
> is safe.  For example, when you issue the CLOSF JSYS to close a file in
> TOPS-20, you are assured that your data is safely out on the disk when
> the JSYS returns.  The close(2) syscall, however, does *not* give you that
> guarantee, and I have gotten screwed at least once like this:
> 
> 	Edit a file with my text editor
> 	Write the file out and exit editor
> 	Power failure (or other abrupt termination of UNIX) before next sync
> 	Reboot, fsck finds my file and claims it has no data blocks
> 	 (the data was floating in the buffer cache when UNIX went down)
> 
> Rick Ace

Not only does UNIX have to have a sync to mark the file as ready for flush
to the disk, some versions wait a further period of time to actually perform
the flush to disK (i.e. sync does not do the flush itself - I know cause it
happened to us).

-- 
-----------------------------------------------------------
David Langdon    Rabbit Software Corp.

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