How to flush data to disk reliably?
From: Grzegorz Kulewski
Date: Mon May 02 2005 - 08:25:32 EST
Hi,
I am writing an app that has log files. These log files must be reliably
and permanently flushed to disk on some points. These log files can be:
a. normal files on some (local) filesytem,
b. some block device (disk/partition).
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)?
What are differences between them? Maybe some other method? Are there any
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?
I am using Linux 2.6. (But I will be glad to hear about differences
between 2.4 and 2.6 in this aspect if there are any.)
Thanks in advance,
Grzegorz Kulewski
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