Favorite operating systems query
dml at rabbit1.UUCP
dml at rabbit1.UUCP
Wed Jun 25 02:32:38 AEST 1986
>
>> >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 at 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).
--
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David Langdon Rabbit Software Corp.
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