Re: How to flush data to disk reliably?

[Alan Cox]

> I am asking how to flush the data from these logs to disk. I know of 
> several methods:
> 1. open with O_SYNC,
> 2. sync(2),
> 3. fsync,
> 4. fdatasync,
> 5. msync (if they are mmaped).
> 
> Which of these are best and most reliable for (a/b) and for (IDE/SCSI)? 

For scsi the combination of O_SYNC and ext3 or fsync and ext3 should be
reliable. fdatasync doesn't write back all the metadata so depending on
the use may not be sufficient. FAT based fs's I believe you need a
current kernel for full O_SYNC behaviour.

> What are differences between them? 

See the manual pages and/or standard.
 
> other precautions that I should be aware of? What about write caches? Are 
> write barriers implemented (on IDE and SATA/SCSI) or should I turn caches 
> off?

SCSI shoule be fine, IDE turn off the write cache.


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