[CentOS] Calling All FS Fanatics

[Feizhou]

Kirk Bocek wrote:
> 
> 
> Feizhou wrote:
>>
>>>> Run XFS without write caching and you should be safe. Are you 
>>>> creating thousands of files?
> 
> I'd still like to know what you mean by 'without write caching.' Do you 
> mean setting it on the 3Ware or is there a FS or OS setting you are 
> talking about?

There are two levels of caching. Hardware and software. Hardware level 
caching involves in your case the 3ware card cache and the individual 
disk caches.

Software level involves the kernel's disk cache.

There are FS level settings available. You can mount the filesystem with 
the sync option which means writes are to be done synchronously and so 
these are not stored in the kernel's cache. There is also dirsync which 
can to used to ensure metadata on files/directories are also written 
synchronously.

You can also do it on a per file level by setting the file's sync (S) 
attribute.

So a completely paranoid setup would include making sure that the 
file/filesystem is sync'ed and also turning off the write cache on the 
hardware. You should be able to set sync at the software level and leave 
the hardware write caching on and see a difference.

You can use Bruce Guenter's framework and test the differences. His is 
pretty simple and you can take out those filesystems that you do not 
want to test.