Feizhou wrote:
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.
So what do *you* do when you disable write caching on one of your systems?